Are you paying too much for your HVAC equipment? How do you know if the quote you received for your equipment is a fair price? Do you have a method of comparing what you have paid for various HVAC equipment with what is being quoted currently?
Keeping track of the cost of HVAC Equipment allows you to quickly provide budgets and check the cost of equipment before you purchase. This database allows you to easily keep track of the most common HVAC equipment.
HVAC Equipment Cost Database
Using an HVAC Equipment cost database will save you a lot of money by avoiding the costly mistake of paying too much for equipment.
Air Conditioners in Historical Pricing HVAC Equipment Database
The HVAC Equipment Cost database keeps track of all your equipment quotes or purchases for easy reference and parametric checks, such as cost per ton ($/Ton), cost per CFM ($/CFM)
For an HVAC Piping & Plumbing Estimator the need for quick budgets for the installation of piping is best handled with a matrix of different material types and sizes. Having an estimating software program can make this process a lot easier as the material pricing is always up to date and can be entered into the matrix quickly.
HVAC Piping Unit Pricing Calculator
UNIT PRICING
Often the requirements of the RFP or bidding instructions will call for the price per foot to install piping beyond that which is required by the contract drawings. Such pricing maybe used for change-orders. Having these numbers available and updated often also gives you a quick reference for budgeting projects. It’s good to know when doing job site comparisons of different piping options or during discussions with engineering, what the cost is for the various piping sizes and types of materials.
HVAC Piping Unit Pricing Calculator for Copper and Carbon Steel from 1/2″ to 14″
COST PER FOOT
The cost per foot for the installation of piping needs to include fittings and hangers prorated into the value. It’s best to look at a standard length of pipe and then figure that you will have a Tee and 90 degree elbow in that length. So for example, using twenty feet of copper water pipe with a Tee and 90 degree elbow plus the hangers to build a unit price would represent a field condition of a fitting every ten feet. For higher density projects like Hospitals you could put more fittings in your unit pricing. Total those cost up and then divide by 20 to derive at a cost per foot for that particular size and material type.
20 feet of pipe + 2 Fittings + 3 Hangers / 20 = Cost per Foot
If the piping is insulated, you can also put the values in for insulation.
The Estimating Wizard provides two spreadsheets for tracking unit pricing, one for HVAC Piping and the other for Plumbing piping. Get a copy and start tracking your cost per foot, or be prepared to give a quick budget based on your knowledge from your spreadsheet of unit prices. Watch the video on the estimating Wizard website and see how quick and easy it is to track the cost per foot for various sozes and material types.
MEP Academy HVAC Piping Unit Pricing Calculator
The MEP Academy provides a spreadsheet that makes calculating unit pricing simple. The spreadsheet is available on the MEP Academy website https://mepacademy.com
HVAC Piping Unit Pricing Calculator Example
In the screenshot above there is a place for you to build your hanger requirements (#1), and a place to put your tax rate and hourly labor rate (#2).
For each size of pipe and material type you would insert the unit cost for Material (#3) and Labor (#4).
Under item (#5) you would build your typical run of pipe and enter the quantity of fittings you might expect for the type of building and system. You would add whatever you think will be required for every so many feet of pipe. In the example above we are showing that for every 20 feet of pipe you will have 1 Elbow and 1 Reducing Tee.
Under item (#6) you would add the cost per lineal foot for insulation if required. You could also look at insulation as a separate value and leave the pipe bare.
Line item (#7) is where you indicate the hanger spacing, and for each hanger you defined under item (#1) you will get the quantity as defined by the linear feet in item (#5) divided by your hanger spacing, which will affect your cost.
Line item (#8) is the calculated cost per linear foot of piping for that size and material type of pipe.
Summary Sheet
After you have all your unit pricing information inputted into the spreadsheet, all you have to do to get a budget for installing piping is to enter the quantity of piping (#9) for each size and material type (#10). The system will automatically calculate the cost (#11) to install that run of piping based on your unit pricing data. The total cost will be shown at the top of the spreadsheet (#12).
The proper sizing and layout of condensate drain lines is important for the protection of property and for the proper functioning of the air conditioning equipment.
If you prefer to watch our YouTube version of this presentation, scroll to the bottom.
Condensate Drain Pipe Sizing
The size required for the condensate pipe is dictated by the local code. Enclosed you will find the requirements for many local codes, but be sure to check your code for your local requirements. If the outlet size of the equipment’s condensate drain is larger than what’s shown in this chart then your required to use the larger outlet size.
Minimum Condensate Drain Pipe Sizing Chart
Slope to be at least 1/8” per foot or 1 percent, that is for every 12” horizontally there must be at least an 1/8” drop vertically.
Condensate drain piping to slope a minimum of 1/8″ per every 12″ horizontal
Attics or Furred Spaces
If the Air Conditioner is suspended above an inaccessible ceiling, such as a gypsum board ceiling or attic space then you will need to provide a means for protecting the building elements from the overflow of the primary drain and for indicating that there is a leak.
Also, drain pans that are poorly drained can cause water to stay in the pan risking the possibility of algae and bacteria growth. Below are some possible solutions, but as always check your local code for the approved method.
Option 1 – Secondary drain pan with drain piping. This would hang below the Air Conditioning unit in case the A/C units primary pan overflowed. Also, there is a requirement to provide secondary drain piping to a point of termination that would provide notification to the occupants that there is a leak, such as terminating above a window or doorway.
Option 1 – Secondary drain pan with piping terminating in observable location
Option 2 – An additional drain pipe connection that sits above the primary drain connection and whereby the secondary drain piping terminates in a location to alert the occupants of the clogged primary drain.
Option 2 – Secondary drain piping connection to primary drain pan
Option 3 – Leak detection device that automatically shuts down the Air Conditioner if the primary drain becomes clogged.
Option 3 – Primary drain with leak detection device
Option 4 – Secondary drain pan with leak detection, located beneath the coil that shuts down the unit upon a leak.
Option 4 – Secondary drain pan with leak detection
The additional drain pan or drain pan connection shall be provided with a drain pipe that will determinate in an observable area, such as in front a window or above a doorway, and be of a size not less than 3/4”. Secondary drain pan shall not be less than 1-1/2” in height and extend 3” wider on each side of the coil or AC unit.
Secondary drain piping terminating above window. Pipe doesn’t have to be visible as shown.
Drain Termination
Where can and can’t you terminate the air conditioners condensate drain piping? There are several options where you can terminate the condensate drain line;
Indirect Drain
Condensate Pump to Indirect Drain
Drywell
Leach pits
Landscaped areas that are properly designed to handle the volume of condensate
To Properly designed stormwater treatment systems.
Indirect Drain
Lavatory tailpiece in the same tenant space as the air conditioner
Laundry standpipe
Janitors Sink
Inlet of Bathtub Overflow – Must be accessible
Collect and send to cooling tower (See description below)
Cooling Coil condensate to sink tailpiece.
The connection to a plumbing fixtures tailpiece has to be made within the same tenant space as the air conditioner cooling coil that is generating the condensate.
Drywell
A drywell can be used for the termination of your air conditioners condensate drain. Check your local code for the specifics, but generally it includes some or all of the following depending on whether it’s for residential or a commercial project:
A minimum size hole, such as 2 foot by 2 foot by 3 feet deep, or a round hole such as 12” diameter by 3 feet deep.
A minimum of 6” of soil or concrete shall provide cover above the rocks
Some form of barrier between the soil and the top of the drywell where the rock begins, such as building paper or plastic
Drywell to be filled with gravel or crushed rock, often with a stated minimum size rock such as 1 inch diameter
The termination of the condensate drain pipe shall connect indirectly to the drywell drain pipe.
The drywell drain pipe to be a minimum of 1-1/2” PVC or other approved material.
Drywell to be at least three feet away from the building structure or any footings.
Drywall for Air Conditioner Cooling Coil Condensate
There are various methods of providing drywells depending on the local code. There are prefabricated drywells that can be used and ones that are made by using a large diameter piece of PVC pipe or similar material.
Some codes will require you to collect the condensate from cooling coil drain pans and return it to the cooling tower if the equipment is served by a cooling tower and the total combined capacity of the HVAC cooling coils exceeds a certain amount like 65,000 btu/hr.
This is a water conservation measure, and there are some exceptions to this requirement, such as if the total capacity of the AC Equipment cooling coils are less than 10% of the total capacity of the cooling tower, or if the location of those AC Cooling coils are in a remote location, far from the tower.
Some locations where you can’t terminate condensate;
Public ways
Sidewalks
Driveways
Alleys
No termination of condensate on public area ways
Excluded from Code Requirements
Excluded from these codes are non-condensing type of equipment like radiant cooling panels that are designed to prevent condensate from occurring by keeping the temperature of the chilled water above the dew point temperature/vapor pressure of the surrounding air. These are system designed to operate in sensible cooling only modes.
Piping Material
The material types that can be used for condensate drain piping varies by jurisdiction but the most commonly cited materials are:
Copper
PVC – DWV
CPVC
ABS – DWV
Polyethylene
Galvanized steel
Cast iron.
Also the use of short radius 90-degree elbows are often prohibited. You can normally use standard fittings until you reach a certain size at which point you might be required to use drainage pattern fittings (DWV)
Traps
Traps are to be installed as required per the manufactures recommendation. No traps are required on the secondary drain pan, this is to allow immediate notification that the primary drain has failed.
Cleanouts
Cleanouts are required in case of plugged drain pipes. Provide as required to prevent the need to cut drain pipes for unplugging. Some of the following maybe used for cleanouts if approved by your local code authority;
Plugged tees
Union connections
Short clamped hoses at the unit (see image above)
When you have more than one air conditioning unit condensate tied to a main condensate pipe, then every change of direction shall have some method of cleanout. Check your local code as this maybe a requirement for even a single air conditioners condensate piping.
Condensate Pumps
Condensate pumps can be used to elevate the condensate vertically to a point where it will then discharge into a code approved gravity sloping condensate drain line. The condensate pump should be interlocked with the Air Conditioning Unit to prevent its operations if the condensate pump is inoperable.
Please remember that code requirements are always changing, so check for the most current code in your area at the time of design and installation. Or ask an inspector for the current installation practice.
Having an MEP Academy Estimating Spreadsheet that automates portions of your estimates, will save you valuable time that could be used to make more sales. All aspects of the cost of furnishing and installing an HVAC and/or a Plumbing system is contained in one spreadsheet made specifically for the MEP industry. For plumbing only see below.
For a Plumbing only Spreadsheet, use this Commercial & Residential Version. Plumbing Only. For a simple Residential HVAC & Plumbing Spreadsheet. Residential version.
Dashboard
The Main Dashboard provides you with all the information you need to make a quick decision on whether to make further adjustments, or if one of the metrics looks out of place based on historical data. The Dashboard gives you a quick overview of all that is going on within the Estimating Spreadsheet.
Estimating Dashboard within the MEP Academy Estimating Spreadsheet
Your MEP Academy Estimating Spreadsheet needs to be able to handle rental equipment, general conditions, subcontractors, piping and plumbing takeoffs, sheet metal, labor rate tables with crew mix capabilities, , and a bid summary. Each sheet in the estimating spreadsheet automatically calculates the values you enter, showing you a new total bid amount.
Will cover portions of the MEP AcademyEstimating Spreadsheet starting at the back of the Excel spreadsheet and working our way toward the front summary page last.
Choose your crew mix based on the level of experience and the different pay scales based on each project. Pick any combination and quantity of tradesman based on the requirements of the project.
Labor Rates and Crew Size within the MEP Academy Estimating Spreadsheet
There is a separate crew labor rate for HVAC Piping Shop & Field, Sheet Metal Shop & Field, and Plumbing.
Enter the project equipment price and labor to rig the HVAC and Plumbing equipment into place. Compare supplier pricing easily side by side. The MEP Academy Estimating Spreadsheet automatically selects the lowest bidder but lets you override that decision.
HVAC Equipment page within the Estimating SpreadsheetHVAC & Plumbing Equipment Sheets
Do you need a jobsite trailer or onsite management? Enter the quantity and level of the staff required to run the project, whether one person or dozens. Set the quantity and duration of each general condition, along with the rate. General Conditions is broken down into three sections as follows: #1 – Management, #2 – Construction Office (Non-Reoccurring Expenses), and #3 – Construction Office (Reoccurring Expenses).
HVAC & Plumbing contractors often subcontract out for Air & Water Balance, Sheet Metal & Piping Insulation, Water Treatment, Building Automation, Excavation and other specialty trades that they don’t self-perform. This spreadsheet was made especially for the HVAC & Plumbing contractor and their most often used subcontractors.
For those contractors that do plumbing the following Plumbing Fixture sheet will give you a place to record your vendors quotes and the labor it takes to install each type of fixture. What is also revealed is the overall cost per fixture.
Plumbing Fixtures page within the Estimating Spreadsheet
Each trade has a specialty sheet for those items that aren’t considered equipment or a fixture, but for which there is a cost impact. The MEP Academy Estimating Spreadsheet includes Sheet Metal, HVAC Piping & Plumbing Specialty sheets.
HVAC and Plumbing Specialty Pages within the Estimating SpreadsheetSpecialty Sheets in Estimate Spreadsheet
Material & Labor Summary Sheets
You will find a Sheet Metal, HVAC Piping & Plumbing material & labor summary sheets where all of the other specialty sheets are summarized for your review and last minute edits. Each sheet will be divided between field & shop fabrication work. The first section covers the field installation items.
Sheet Metal Material and Labor Summary – Estimating Spreadsheet
Each of the field labor summary sheets contain a row to add for the following
Material Handling
Consumables
Punch List
Cleanup
Detailing
Supervision
Shop Fabrication Summary Section
For those of you that have a fabrication shop, there is a section to add material and labor.
Shop Fabrication Summary
Rentals
For those HVAC air conditioning and Plumbing projects that require a crane, fork lift, scissor lift or any other equipment that you don’t own but will be required on the project. Having a spreadsheet that maintains a list of the most common equipment you normally rent along with their rental rate will save you time and money while avoiding having to call for pricing on every job.
Rental Sheet in Estimating Spreadsheet
Engineering
If you do your own design then you should have a sheet of each of the personnel responsible for spending time on the engineering task. If you’re doing design/build work, but don’t do the engineering yourself, but hire a third party, then you should add some engineering review time. It’s your responsibility to manage your third-party engineer to make sure they design within your cost parameters.
All of your estimates are summarized on the last tab of the MEP Academy Estimating Spreadsheet for easy review. You can quickly scan each of the categories to see where all the project cost has shown up. There is the labor and material summary for HVAC Sheet Metal, HVAC Piping, and Plumbing and another section for Subcontractors, General Conditions, Rentals, etc.
Estimating Spreadsheet Summary PageMEP Academy Estimating Spreadsheet Summary
The MEP Academy Estimating Spreadsheet contains a bid risk assessment form that rates the success of winning any particular project that you are contemplating pursuing. The risk assessment form will help you determine if the project is worth bidding based on a set of questions that rate your answers.
Bid Risk Assessment
The answers to these questions will give you a score from which you can use to see how the project rates on a scale of risk and reward. The total risk assessment score will also inform you which level of approval is required within your company depending on how you rate your risk values as the example shown below. The total score is 25, which according to this contractor would require the Vice President to sign-off on the project or approve the decision to pursue bidding on the project.
The MEP Academy Estimating Spreadsheet is used to gather all the information for estimating a project, putting it into a format where you can make quick adjustments and decisions while the spreadsheet gives you an immediate update on the price.
Purchase this spreadsheet at its currently reduced price of ONLY $245.00, which usually sells for $599.00
Watch the YouTube video below to see the MEP Academy Estimating Spreadsheet in action.
How Plate Heat Exchangers Work. In this presentation we’ll learn How Plate and Frame Heat Exchangers work. These maybe referenced on engineered drawings as HEX, HX, PHX or PHE. Plate and frame heat exchangers are used in the HVAC and Plumbing industry for the transfer of heat from one system to another without the fluids meeting each other. The purpose of the heat exchanger is to transfer thermal energy from one system to another without the fluids contacting each other.
If you prefer to watch the Video of this Presentation, then scroll to the bottom or click this link. How Plate Heat Exchangers Work
The two most common types of heat exchangers are the shell and tube heat exchanger and the plate and frame type that we are going to discuss here.
Heat Exchanger Types (Shell and Tube)(Plate and Frame)
A Plate and frame heat exchangers can be used for a water side economizer, where one side is connected to the cooling towers, and the other side is connected to the chilled water distribution piping. This keeps the cooling tower water separate from the chilled water loop.
Water-side Economizer using a Plate and Frame Heat Exchanger
Parts of a Plate and Frame Heat Exchanger
There are very few parts for a Plate and Frame heat exchanger which can be used with fluids or gases. They will contain threaded or flanged inlet and outlet connections for both the primary and secondary sides of the heat exchanger. One set of inlet and outlet connection will be considered the hot side and the other the cold, as heat will move from the warmer to the colder fluid or gas, hence exchanging heat.
Plate and Frame Heat Exchanger components
The plate and frame heat exchangers are like a sandwich, where you have two slices of bread or in our case two thick sheets of mild steel that form the ends, with layers of thin, gasketed, corrugated plates sandwiched in-between. One end is a fixed plate, while the other end is movable pressure plate. The fixed plate end will have holes in it for the piping connections. For the HVAC and Plumbing trades, the use of stainless-steel plates is common and can be either 316 SS or the less expensive 304 SS.
There are top and bottom carrier bars between the two end plates from which all the gasket plates are supported from which also provides a method for their alignment. The gasketed plates are grooved along their top to fit onto the carrier bar.
Heat Exchanger with Fixed and Moveable Plates
Then there is a long clamping or tightening bolts that run the length of the heat exchanger from one end plate to the other that will tighten all the plates firmly together. There is a gasket on one side of each plate that when the bolts are tightened, all the plates are squeezed together between the two end plates ensuring a watertight seal. The gasket can be made of nitrile or EPDM, both synthetic forms of rubber.
How Plate & Frame Heat Exchanger Work
The warm fluid will enter the inlet on the primary side of the fixed end where the gasketed plates will route the fluid through the first plate and every other plate or odd numbered plate and then exit the outlet piping connection. The cold fluid will enter the inlet on the secondary side of the fixed end and be routed to the second plate and every other plate or ever even numbered plate, before exiting the outlet pipe connection on the fixed end.
Heat Exchanger Plates
The primary fluid never mixes with the secondary fluid, they just transfer their heat between the plates surface area in an alternating pattern of hot and cold plates. The hot fluid will give up some of its heat and become cooler, while the cold fluid will pick up some of that heat and become warmer.
Remember that the natural laws state that heat will leave the warmer fluid and transfer to a cooler fluid in its attempt to reach equilibrium along as there is a temperature difference between them. The heat given up by the warmer fluid is equal to the heat gained by the cooler fluid, minus any heat lost to the surroundings.
The plates are thin and close together to provide good thermal contact and heat transfer. The thin metal and large surface area provides a means for high thermal conductivity and heat transfer between the two fluids.
Heat Exchanger Plates in a Plate & Frame Heat Exchanger
The plates come stamped with many different patterns on their face and will have four holes in their corners where the main fluid or gas flows. The patterns are designed to increase turbulent flow which increases the rate of heat transfer and prevents the accumulation of mineral buildup on the plates. The various stamped metal patterns also provide rigidity to the plates.
There will be a starting and ending plate. These plates prevent the fluid or gas from getting behind them and in-between the fixed and movable end covers.
Increasing Heat Exchanger Capacity
One of the benefits for using a Plate and Frame heat exchanger is the ease by which additional capacity can be added. There are several methods that can be deployed to increase the capacity of a heat exchanger.
One method is to increase the number of plates which will increase the heat exchangers capacity, or if you want to reduce capacity, then remove some plates.
Single Pass Heat Exchanger
Increase the number of passes that the fluid travels through the heat exchanger. A single pass heat exchanger is where the fluid passes through a single plate and then exits. A multiple pass heat exchanger will send the fluid through more than one plate before it exits. A multiple pass heat exchanger gives the fluid more time to transfer heat.
Multi-Pass Heat Exchanger
Another way to increase capacity is to increase the flow rate through the plates.
For higher pressure systems there is the option is to use brazed, welded or fusion-bonded plates.
Flow Patterns through Heat Exchanger
There are three common methods of how the flow of fluid traverses the plates in relationship between the primary and secondary fluids. They can flow in the same direction which is considered parallel flow. They can flow in opposite direction to each other and that would be counter flow. Then there is cross flow, where one fluid travels perpendicular to the other.
Heat Exchanger Primary and Secondary
Where can they be used?
Here is a possible list of places you could find plate and frame heat exchangers in the HVAC and Plumbing Industry. For areas where freezing is possible, then the use of a Water/Glycol solution can be used but will require a slight larger heat transfer area.
Heat Recovery Applications like heat from a chiller or generator
Water-side economizer
Swimming pools or Spa’s
District Heating or Cooling
Preheating of Domestic Water
Preheating of Boiler Feedwater
Process heating or cooling
Solar Heating
Water-Cooled Heat Pumps
Advantages of Plate and Frame Heat Exchangers
They take up less space.
They weigh less.
They are more efficient.
Easy to clean plates.
Longer intervals between cleanings.
Less space required for dismantling.
Easier to increase capacity with gasketed versions.
How an Air Side Economizer works. There are energy codes that mandate the use of an air-side economizer for HVAC equipment over a certain size. An economizer reduces energy consumption by using the outdoor air for cooling in mild or cold weather instead of mechanical cooling. We’ll cover how an air-side economizer works and show you three different relief air options.
If you prefer to watch the Video fo this presentation, then scroll to the bottom or click on this link How an Air Side Economizer Works.
Air-side economizers are used with Packaged Units, Split Systems and Air handlers of all sizes. When the outside air temperature is below the return air temperature, then outside air can be more energy efficient to use for cooling then mechanical cooling.
Here is one control layout of many for controlling an economizer. We have an economizer controller which can be integrated into the economizer section or as a separate controller. Next there will be a thermostat in the space, and a Supply Air Temperature sensor in the supply air discharge duct.
Air Economizer with Relief Air Damper
There is a Return Air Temperature sensor in the Return Air Duct. The Economizer Controller will need a transformer to provide 24 volt power. The system will need an outside air temperature sensor and Mixed Air Temperature sensor, and communication with the damper actuator, and the power to modulate the damper.
Economizer Relief/Exhaust Air
One of the important design considerations for an outside air system is how to control building pressure when excess outside air is brought into the space. There are three common approaches for the design of the relief air system. Some engineers may refer to this as exhaust air. The Relief or exhaust air needs to be considered to avoid over-pressurizing the space.
Packaged HVAC Unit with an Air Side Economizer
Barometric Damper (Backdraft Damper)
One method is to use relief dampers that are set to open when the building pressure reaches a certain level, such as 0.05” or 12 Pascals. This pressure will be set just below the maximum allowable for the pressure in the building space. This can be a barometric damper with an adjustable weight for varying the pressure relief setting.
As the economizer starts to open the outside air damper, it will modulate the return air damper in the opposite direction, causing the pressure in the building to increase. When the pressure reaches the preset pressure on the barometric relief damper it will begin to open, allowing air to escape the building. When the outside air damper is fully open in 100% economizer mode, the return air damper will be fully closed, causing the pressure in the building to open the barometric damper, allowing excess air to escape the building.
Building Pressure relieved with the use of a Barometric Damper
There are many sequences of operation for controlling an economizer. Each situation is unique to the geographical area and desired indoor conditions. We’ll explain the basic premise of the economizer cycle using the supply air temperature setpoint as the controlling factor.
If we set the supply air temperature to 55 degrees Fahrenheit (13 degrees Celsius), then the economizer controller will use this to determine the position of the dampers, along with all the other input points like an “Outside Temperature Sensor”, “Return Air Temperature Sensor”, Supply Air Temperature Sensor”, “Mixed Air Temperature Sensor” and the room thermostat or main controller. It will send an output signal to the damper actuator for the correct mixture of outside air and return air to meet the supply air setpoint.
If the outdoor temperature is below the return air temperature then the outdoor air can be used in situations where a differential dry bulb type of economizer would be used. If in more humid areas, then the outdoor temperature would need to be much lower than the return air temperature to compensate for the increase in humidity.
The purpose of course is to avoid using the compressor or chiller for cooling in order to save energy. If the outside air damper is 30% open, then the return air will be 70% open, so that we have 100% of the air needed by the supply fan. If the outside air damper opens to 80%, then the return air damper will close down to 20% open. If the outside air is not within the useful range of the economizer, than the outside air damper will be set to its minimum setpoint to meet ASHARE 62.1 requirements for ventilation air.
The use of a barometric relief damper is the least expensive option of the three presented here, as there is no electrical connection, sophisticated controls or motorized damper.
Air Side Economizer in a Classroom with Relief Air (Barometric Damper)
Barometric dampers are used on small systems, such as a classroom as shown here. When the classroom becomes over-pressurized, the barometric damper opens without the assistance of electrical power.
Economizer with Relief Fan/Powered Exhaust
Another method of relieving the building pressure caused by the economizer is to use a relief fan as shown here. When the economizer is operating the relief fan will be engaged and cycle on and off with the economizer. There has to be a method of controlling the relief fan according to the building pressure and the amount of outside air that is brought in during economizer mode, which can varying from 100% down to the minimum position according to ASHRAE 62.1.
Air Economizer with Powered Exhaust / Relief Fan
Remember that the economizer is modulating the volume of outside air that is coming into the building to meet the current demand which is fluctuating. This will require that the relief fan or fans be cable of some form of variable volume. This can occur by staging multiple relief fans in a large system, or with the use of a variable frequency drive to vary motor speed.
Economizer with Return Fan
The addition of a return fan is important with ducted systems that have a large pressure drop to overcome. With the addition of a return fan, the supply fan can be slightly smaller as it doesn’t need to overcome the static pressure of the return ductwork.
Air Side Economizer with Return Fan
Controlling Economizers
Economizers can be controlled using differential dry bulb temperatures or enthalpy, which is both temperature and humidity.
Using differential dry bulb will activate the economizer when the outside air drops below the return air.
When using differential enthalpy the economizer is activated when the outside air enthalpy drops below the return air enthalpy.
We’ll use an example of a differential dry bulb economizer.
In heating mode the outside air damper is at minimum position according to ASHRAE 62.1 ventilation requirements. The minimum outside air mixes with the return air. When cooling is required and the temperature is between 35 and 55 F (2 C to 13 C) the compressor can shutoff and the outside air can mix with the return air to maintain the supply air temperature setpoint. The outside air damper will modulate from its minimum to maximum position in order to satisfy the supply air temperature setpoint.
As the outside air temperature rises further somewhere between 55 F to 75 F (13 C to 24 C), the outdoor air may not be sufficient to reach the supply air setpoint, so the mechanical system will start up and run the compressor or modulate the chilled water valve. This is considered an integrated system, one where the economizer and mechanical cooling work together to satisfy the setpoint temperature. The outside air damper is 100% open and the mechanical system modulates to reach the supply air setpoint.
The economizer will have a high-limit shutoff temperature where the economizer will reset itself to the minimum position to meet ASHRAE 62.1 for minimum ventilation. This can be 75 F (24 C) or slightly lower depending on geographical area.
ASHRAE 62.1 and (0.1 Requirements
ASHRAE 62.1 requires a minimum amount of outside air for ventilation purposes, but with the use of an economizer, outside air can be used for cooling when conditions are right and provide 100% of the air. The economizer can come as part of a packaged HVAC unit or as stand-alone components.
ASHRAE 90.1 2019 6.4.3.4 Ventilation System Controls requires that all outdoor intake and exhaust systems be equipped with motorized dampers that will automatically shut when the system or spaces served are not in use. Outdoor air and exhaust/relief dampers shall be capable of and configured to automatically shut off during preoccupancy building warm-up, cool-down, and setback, except when the supply of outdoor air reduces energy cost or when outdoor air must be supplied to meet code, except that gravity back draft dampers are acceptable for exhaust and relief in buildings less than three stories in height located in Climate Zones 0, 1, 2, and 3. This means that if your building is three stories or more than a motorized damper maybe required.
Bypass Damper HVAC VVT System. You might be familiar with a Variable Air Volume VAV System, but we’ll explain the less energy efficient version that tries to mimic the VAV system. A Variable Volume/Variable Temperature system uses similar components to that of a VAV but is not as effective at saving energy. We’ll show you the control strategy for a commercial and residential application using a Bypass Damper.
If you prefer to watch the Video of this presentation, then scroll to the bottom or click this link. Bypass Damper HVAC VVT System
Commercial VVT System with Bypass Damper
The constant volume air conditioner or heat pump serves several zones, with each zone having their own zone damper and controller. When the zone dampers start to close the static pressure sensor picks up an increase in the duct static pressure and sends a signal to the bypass damper controller to modulate the damper open.
VVT System with Bypass Damper
If we look at an example using a 3,000 CFM (84 M3/M) constant volume air conditioner with three zones each sized for 1,000 CFM (28 M3/M) at peak load, and with a Bypass Damper that is closed because all of the Air Conditioners air is being delivered to the zones.
If the controller for Zone Damper #1 required less air and the damper modulated down to deliver only 500 CFM (14 M3/M), then only 2,500 CFM (70 M3/M) of the total air from the air conditioner is needed by the zones.
VVT System using a Bypass Damper for Static Pressure Control
As the Zone Damper #1 modulates to partially closed, the pressure in the supply duct will increase. This increase in duct pressure will be picked up by the Static Pressure Sensor which will send a signal to the Bypass Damper controller to modulate open to allow the excessive air, in this case 500 CFM (14 M3/M) to pass from the supply air to the return air duct without entering any of the zones as shown above.
VVT System Diagram with Zone Dampers Closing and Bypass Damper Opening
If Zone Damper #2 was to also reduce the amount of air delivered to the space in the same amount, then the duct pressure would increase and the static pressure sensor would send a signal to the Bypass Damper to open further.
Then if Zone Damper #1 closes completely as the occupants have left the space, then the Bypass Damper will have to Bypass all the air that would have gone to this zone.
VVT System HVAC Diagram with 50% Bypass Air
Remember that the air conditioner is a constant volume unit and has no way to reduce the air delivered by the unit. This air has to go somewhere, so it is bypassed from the supply air to the return air without entering the space. What happens is that the air becomes cooler or warmer because it hasn’t rejected or absorbed heat from the space.
Residential VVT System with Bypass Damper
Anyone that has lived in a two story home knows that its best served by two separate HVAC systems. Some have tried to modify the one Air Conditioning System by adding individual zone dampers, one for the first floor and a separate one for the second floor.
Residential VVT System for HVAC Control using a Bypass Damper or Barometric Damper
When the residents go to sleep at night on the second floor, the first floor damper can close. Since this is a constant volume air conditioner the additional air will be bypassed to the return air plenum or to a dump zone. The dump zone should be a hallway or unoccupied area of the house as the extra air dumped in this area will cause temperature problems, such as excessive heating or cooling depending on the mode of operation.
HVAC VVT System in a Residence with Bypass Damper
We show a motorized bypass damper in this diagram, but a barometric damper is often used. The barometric damper is set to open when the pressure increases to a certain amount, allowing air to bypass the supply and be redirected to the return.
The other way is to directly connect the bypass duct to the return duct which avoids excessive temperature swings in a dump zone. There are many variations of this installation in order to achieve some form of zoning. The best system layout would be to have two separate HVAC systems, one for the first floor and a separate one for the second floor.
VVT Controls
The installation of the controls for a VVT System with a Bypass Damper is simple compared to a standard DDC system for a VAV system. First will install zone controllers for each zone that are connected to the zone dampers using 20ga 3 wire shielded cable.
VVT Control System
Next we need to install a 120 volt main feeder to power all the dampers. A 120v to 24v Transformer will need to be installed to power the Bypass damper, and transformers for the zone dampers. All the zone dampers can be daisy chained together using the same 20ga 3 wire shielded cable, and then connected to the Air Conditioner. A main controller can be installed that allows for reading of all the status points of the system. And lastly there will be a static pressure sensor installed. There are other optional control items that can be installed like a CO2 sensor for carbon dioxide sensing and ventilation control, heating hot water valve actuators for Zones with Heating Hot Water. The system can also be monitored by a Building Management System.
Variable Volume
A VVT system uses zone dampers so that each zone can adjust the volume of air that it receives based on its heating or cooling load. Each zone will have its own controller that will adjust the air volume to its zone based on the demand.
What makes the VVT system different from the more efficient VAV system is the use of less expensive constant volume Air Conditioning Unit and less sophisticated controls.
The VVT system uses a bypass controller to modulate the bypass damper to allow any unused supply air to return to the system. When supply air zone dampers start to close the constant volume air delivered by the air conditioner needs to be maintained by bypassing the excessive air. The Air Conditioning Unit is sized to handle the peak load, which is only needed a few times a year. The excess air needs to be bypassed and rerouted from the supply back into the return air system.
The use of a bypass damper allows for the use of the less expensive constant volume units when compared to the cost of a VAV system. The bypass damper must ensure that the constant volume unit receives the minimum amount required for it to function properly. If the minimum amount of air is not allowed over the coil, the coil could freeze up. The bypass damper also allows the ductwork to be installed using low pressure duct, as the bypass damper prevents buildup of static pressure in the ductwork. Excessive static pressure could cause the joints or seams of the duct to come apart, creating leaks.
The bypass controller uses a duct static pressure sensor installed in the supply air ductwork. The controller is set by the user to maintain a minimum and maximum pressure in the supply duct main. As the static pressure in the duct increases due to zone dampers closing, the sensor picks up an increase in static pressure and will modulate to bypass the excess air.
There are two simple setups for the bypass air, it can either be ducted directly into the return air duct, or it can be bypassed into the return air plenum if the plenum is rated and approved for this use.
Because the fan is always running at constant speed, there is no fan energy savings when the zone dampers start closing, as opposed to a true VAV system where the fan speed is reduced.
Variable Temperature
The system temperature will also vary as the bypass damper passes excessive air from the supply back to the return. This excessive bypass air is the quantity of CFM supplied by the constant volume unit that’s above what is needed by the zones at any time. As this cold air is not sent to the zones to pick up heat from the space it returns to the air conditioner cold.
Because the volume of return air is reduced due to the zone dampers partially closing, the excess cold supply air is bypassed back to the unit without picking up heat. This raises the supply air temperature, hence the variable temperature part of the system.
3-Way Switch Wiring Explained. How Three-way light switches work. In this presentation we’ll learn how to control a light using a 3-way switch, which is convenient when there are two or more entrances to a room, or an upper and lower stairwell. We’ll show several different wiring configurations.
To watch the FREE YouTube version of this presentation, scroll to the bottom or click on the following link. 3-Way Switch Wiring Explained
Electrical Safety Warning
Whenever working with electrical be sure to shutoff the power at the electrical panel, and hire a qualified electrician to do the installation if you are not confident that you can do the job safely. Electricity can kill.
3-Way Switch for Controlling a Light or Fan
How do 3-Way Light Switches Work?
If we look at a 3-way switch, we’ll see that it has four terminal screws. We have two traveler terminals, which are usually identified by their light color of bronze or copper, a ground terminal in green, and a common terminal often a dark color. A 3-way switch won’t have an on/off designation that can be found on standard switches, as either position could be on or off.
Within the switch either one of the traveler terminals is connected to the common terminal, which can make or break the circuit depending on the position of the other switches traveler terminal matching or not. Its like the game of concentration where you turn over two playing cards trying to get them to match. When the two separate 2-way switches match on their traveler wires the light goes on, when they don’t match the light goes off. They can match with both on red or both on black, but not black/red or red/black.
The two traveler terminals can be on the same side of the switch or on opposite sides of the switch depending on the switch manufacturer.
3-Way Switch Example #1
With this layout we have the light fixture between the two switches.
The incoming electrical power will connect to the common terminal of switch #2. Then we route the Black traveler wire for switch #2 to switch #1. We do the same thing for the Red traveler wire. From the common terminal on switch #1 we connect to the light. We bring in the neutral wire from the power source and connect directly to the light. We also bring in the ground wire from the electrical panel and connect to each of the switches.
3-Way Light Switch with light off.
If we remove the switch covers and look inside we can see how these 3-way light switches work. Inside is a single pole double throw switch which provides each switch with an option to connect the common terminal with either the red or black traveler terminal.
When both switches are not in the same configuration, such as shown below we have one switches common connected to a black traveler and the other switch connected to a red traveler terminal. If we follow the power from the source, the black common wire from the electrical panel connects to the common terminal on switch #2, then passes through the switch to the black traveler terminal and then onto switch #1 where it dead ends.
3-Way Switch Wiring with switches in opposing positions
If we flip switch #1 to the black traveler wire then the light comes on as the electrical circuit has a complete path through both switches to the light.
3-Way Switch Wiring Explained
The process of turning on and off the light can occur from either switch, as we show here we now flip switch #2 to break the electrical circuit and shut the light off. In order to turn the light back on we have two options, we can flip switch #1 to the red traveler terminal so that it matches switch #2, or just flip back switch #2 to the black traveler terminal.
3-Way Switch Example #2
Depending on the layout of the space and where the wiring originates from, there are several versions of how the wiring can be done. We’ll show how to wire a 3-way switch with both switches wired before the light.
Will install a light fixture, and two switches. From the power source we’ll bring the black hot wire to switch #2 common terminal. Note, that this wire is usually black, but your wire could be another color.
3-Way Light Switch Wiring Diagram
Then we’ll run a black traveler wire from 3-way switch #2 to the same terminal on switch #1, this could be from left side of the switch to the left side of the other switch. Then we install an outlet box and run the black wire from the dark common terminal screw on the bottom of switch #2 to the light fixture. Now we have one complete path from the source all the way to the light.
Next, we install a red traveler wire from the right side of switch #1 to the right side of switch #2. This gives us a second optional path to the light through the red traveler wires from the black hot wire brought to the common terminal.
Next, we install the incoming white neutral wire which is usually white, and we connect to the light fixture. Then we install the green ground wire from our source to the outlet boxes ground terminal, and then to each of the ground terminals on the switches. The ground is usually an insulated green wire or can be bare copper wire. In the fixtures electrical box there should be a place to land the ground wire.
We have 4 wire connections on each switch. Two travelers, one common, and one ground.
When we turn on the power and both switches have the same traveler terminal connected to common then the light will come on as shown above where both black traveler wires are in the same position. This could be either both black or both red travelers in the same position.
3-Way Light Switch Wiring Schematic
When one of the switches is flipped so as there is no matching traveler wire that provides a complete path to the hot common wire the light goes off as shown here with switch #1 being flipped off. The 3-way switch doesn’t indicate the light is on when the switch is in the up position, and off when in the down position. The light being off or on is determined when there is a matching pair of traveler wires that provide a complete path for the power to the light.
Inside the 3-Way Switch
If we looked inside we could see that each switch has a single pole and a double throw, meaning that the switch has two options, to either have the common connected to traveler terminal #1 or 2.
When both of the switches are on the same traveler terminal as shown here, the power runs through to the light. If either of the switches changes position then the light will go off. The electrical power comes through the black common wire connected to switch #2, and uses the red wire to reach terminal #2 on switch #1, where it flows through the common wire to the light, making a complete circuit.
Stairwell Example
First we mount a light above or stairwell and install a switch at the top and bottom of the stairwell. We bring in power using a black wire and connect to the common terminal on switch #1.
3-Way Switch in Stairwell
From switch #1 we run a black traveler wire to switch #2’s traveler wire terminal, and from the common on switch #2 we run a black wire to the light fixture. Then we run a red, second traveler wire from switch #1 to switch #2. We install a neutral wire from the electrical panel to the light fixture. Lastly we provide a green insulated ground wire from the panel to each of the light switches.
How Steam Traps Work. We’ll explain the important job of steam traps and how the three most common steam traps work. We’ll also show you examples of where they’re used in the HVAC industry.
if you prefer to watch the video of this presentation scroll to the bottom or click on this link. How Steam Traps Work.
When steam gives up its heat it turns into condensate, which must be removed from the system. The rate of heat transfer through the heat exchanger is highest when the heat exchanger is full of steam. If condensate wasn’t drained out of the system, and it collected in the heat exchanger, then the rate of heat transfer would drop.
Remember that a pound (0.45 kg) of water or condensate holds 1 Btu (1.5 kj) as it gives up its heat one degree (0.55 K), and that steam gives out approximately 1,000 Btus (1,055 kj) for every pound (0.45 kg).
IThe Heat Content of Steam vs Condensate
if condensate is allowed to sit in the heat exchanger the system will lose capacity. Therefore, it’s important to make sure that the condensate is quickly removed while not allowing the steam to escape without first transferring its heat.
Condensate Water Hammer
Condensate if left to collect in the pipes could cause problems such as water hammer noises, where a high velocity slug of condensate water is slammed against fittings or equipment. This is like a tidal wave in the pipes. The energy is dissipated onto the piping components and is noticeable by the noise it makes or the rattling of the pipes.
Steam Condensate Water Hammer caused by Slugs of Condensate
When the steam boiler starts the system will be full of air and non-condensable gases that need to be vented out of the system. If a steam trap fails to remove air from the system, the air and non-condensable gasses will reduce the heat transfer rate of the heat exchanger. Non-condensable gases behave like an insulator, thereby reducing the heat transfer rate.
The steam traps job is to remove condensate, air, and non-condensable gases, while preventing steam from leaking past it in a steam system. For the basic understanding of a steam system see our video on Steam Heating System Basics.
There are three main types of steam traps, but they all require a differential pressure between the inlet and the outlet of the steam trap. We’ll cover how each of the three steam traps categories work.
Mechanical Steam Traps
The density difference between the steam and condensate is how a Mechanical steam trap works. Steam in the form of vapor is less dense than that of liquid condensate which makes the use of a float as an effective means of control. The float and thermostatic (F&T) trap and the inverted bucket trap are the two most common mechanical steam traps. These traps use floats that rise, and fall based on the amount of condensate, and either open or close the trap.
Float and Thermostatic Steam Trap – Mechanical Steam Trap
When the condensate level is high in a float & thermostatic trap, the float rises and opens the trap to allow condensate to flow out. When the condensate level drops, so does the float which causes the trap to close.
With an inverted bucket trap, steam will push the bucket upward closing the trap, while condensate will pull the bucket down opening the trap.
These steam traps open and close based on the density of the steam and condensate being different. With the F&T trap the heavier condensate lifts the float, while with the Inverted Bucket the heavier condensate sinks the float.
Thermostatic Steam Traps
The temperature difference between steam and condensate is how a thermostatic steam trap work. It’s based-on temperature. After the condensate forms its temperature drops below that of the steam, and after a certain drop in condensate temperature the trap opens. When steam first condenses its temperature is the same as the condensate. This will require that the condensate cool further before the trap opens.
Thermostatic Steam Trap
There are various substances used as the controlling element in thermostatic steam traps, such as fluids and metals.
The bimetal type thermostatic steam traps uses the differing coefficients of expansion of various metals. When two metals are attached together, and one expands at a different rate then the other based on temperature, this can be used to open and close a steam trap. As more and more steam enters the trap, the bimetal heats up and expands while pulling up on the stem of the valve that closes the steam trap, and when it cools down it opens the trap. The presence of steam will cause the bimetal to bend in a certain direction and close the trap, while the cooler condensate will contract the bimetal to open the trap.
When the boiler starts up after being off, the air, condensable gases, and the condensate in the system will be pushed through the open steam trap.
Thermodynamic Steam Traps
The Velocity difference between steam and condensate is how a thermodynamic steam trap works. Steam moves at a greater velocity than condensate. The only moving part in this thermodynamic steam traps is the disc, which moves up and down, opening and closing the port for condensate to flow through.
Thermodynamic Steam Trap
When the steam system is started, the cool condensate and air is pushed by pressure into the trap, causing the disc to move upward, allowing the condensate and air to pass through.
As hot condensate moves through the steam trap some of it flashes into steam, causing the pressure to drop below the disk, which causes the disk to drop.
As the condensate heats up and flows through the trap it cause steam to flash under the disc, which drops the pressure causing the disc to drop lower towards the seat or opening. As this is occurring the flash steam on top of the disc is pushing the disc closed. This traps the flash steam in the upper chamber, which causes an equalization of pressure on both sides of the disk, preventing any more condensate from passing through.
Flash steam in the upper chamber condenses, causing the disc to be forced up, while allowing condensate to enter. This process repeats itself over and over again.
Steam Heating System Basics. Learn how steam systems work and where they’re used in the HVAC Industry. We’ll show you three systems that use steam for heating.
If you prefer to watch the Video of this presentation, than scroll to the bottom or click this link. Steam Heating System Basics.
Steam heating systems are found in Commercial, Residential, and Industrial Facilities. They can be found in central plants of large University Campuses and in District Steam Distribution systems.
Steam is used in laboratories, breweries, food processing, industrial plants, in hospitals for sterilization, and in the production of electricity through steam driven turbines. There are two basic system types, direct and indirect steam systems.
We’ll discuss the basic indirect steam heating system.
Steam is moved through the system of pipes by the pressure created when water is vaporized into steam. There are no pumps required, as the higher pressure within a steam system causes it to move through the pipe, valves, and equipment.
We can witness this on any stovetop when a tea kettle whistles. As the water turns to steam it seeks to escape the tea kettle through the small opening and whistles as it escapes.
Condensate from the steam condensing needs to be brought back to the system for reuse unless the steam is used for a process. The condensate can be brought back by gravity or with the use of a condensate return pump.
When heat is added to water its temperature will rise until it hits the point of evaporation, at this point it changes from a liquid into a vapor or steam. This occurs at 212 Fahrenheit or 100 degrees Celsius at normal atmospheric pressure.
Steam Boiler feeding a Steam Radiator
If we enclose the water within a steam boiler with no opening to the atmosphere, the steam will increase the pressure within the system as the molecules move faster and faster, colliding into each other and the walls of the boiler looking for a lower pressure escape route like the hole in the tea kettle.
If we connect piping to an opening in the steam boiler the steam will exit the boiler into the piping without the need of a pump, but just by the pressure created by the steam.
Steam Heat Exchanger for Heating Hot Water
Here we use a steam boiler to feed the primary side of a heat exchanger. The steam will transfer heat to the secondary loop which is feeding the heating hot water coils in Air Handlers. The steam gives up its latent heat and condenses as the heat is transferred to secondary side of the heat exchanger.
Steam Heat Exchanger serving a Heating Hot Water Coil
To make sure that we are not letting steam into the condensate return we install a steam trap. The steam trap prevents steam from passing through and only lets condensate through. See our video on How Steam Traps Work for a explanation of steam trap types.
On the secondary side of the heat exchanger is a separate loop of water that serves to heating the air in the building air handlers.
If we look inside the heat exchanger, we can see that the primary and secondary piping never mix. The steam enters the heat exchanger as steam and leaves as condensate, while the secondary loop heating hot water is moved by a pump through the system.
Steam Heat Exchanger
The secondary loop heating hot water return enters the bottom of the heat exchanger and picks up heat from the steam and leaves through the top to the air handlers heating hot water coil.
The steam boiler doesn’t need a pump as the molecules are moving fast and exerts pressure on the walls of the boiler and when the piping is connected to the boiler than pressure pushes the steam out of the boiler and into the pipes just like a tea pot that is boiling, and the steam is escaping out of the spout whistling as it exits.
Now we’ll add another piece of equipment requiring a supply of steam.
Steam Heating System Basics
We’ll have to redo the steam piping to make connections to the domestic system. We’ll install a new steam main and make a connection to the Heat Exchanger making sure to come off the top of the steam main, which we’ll explain why in a minute. Next, we’ll connect the domestic hot water heater and storage tank.
We’ll need a steam trap at the end of any main steam run to allow only condensate to pass through. A main condensate pipe needs to collect all the condensate from any steam systems, here we show a simple system.
Next, we’ll connect the condensate from the heat exchanger to the main condensate line and be sure to install a steam trap to prevent steam from escaping. Allowing steam to escape would be a waste of energy. We’ll also connect the condensate from the heat exchanger that feeds the domestic hot water system and include a steam trap.
We need to connect the main steam line through the steam trap to the main condensate piping going back to the boiler.
Now we can feed the building with domestic hot water, including a return line, and makeup water. This completes a simple layout of a steam heating system. Of course, there are many other components to a steam system which we’ll cover in a more advanced video on steam heating, but this gives you a simple view of what it might look like.
Why Tap Steam off the Top
It’s important that any steam branch line be taken off the top of the main steam pipe in order to prevent pulling condensate into the branch. As you can see the steam will rise to the top because of its lighter density and higher temperature.
Steam off the top of the Main and Condensate off the bottom.
For similar reasons you want to make any condensate branch connections off the bottom of any steam line or system to ensure that you are only pulling condensate. And all condensate branches should contain some type of steam trap to ensure that only condensate passes through to the condensate system.
Why use Steam?
Steam has a higher heat content then hot water, which means it can carry a lot more heat in a smaller volume. This heat is in the form of latent heat, which is the change in state from liquid to vapor, and from vapor to liquid. This helps keep the pipes smaller. Steam is water based, so its non-toxic nor flammable, although it’s very hot and will need insulation on the distribution piping to avoid heat loss and prevent someone for getting burned if touched.
The main components of a steam system are the steam boiler, the distribution piping, the steam traps, and the heat exchanger or equipment that requires the use of steam. There will need to be a source of fuel, such as natural gas or fuel oil. A means for makeup water supply, and for boiler blow down to remove unwanted dissolved solids.
This is the basics of a steam system. We’ll get into the details of how each of these components work in other videos.
