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How a Condensing Boiler Works

MEP Academy Instructor

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May 15, 2022

How a Condensing Boiler Works. We’ll explain how condensing boilers or condensing heaters work and their residential and commercial applications. Why are condensing boilers more efficient than the standard non-condensing boilers? We’ll explain what you should think about before adding a condensing boiler to your home or commercial property.

To watch the FREE YouTube version of this presentation, scroll to the bottom.

Before we explain how a condensing boiler works, it’s best to understand how a conventional non-condensing boiler operates.

Checkout these Condensing Boilers here

How Standard Boilers Work

The conventional non-condensing boiler uses one heat exchanger to transfer heat between the burning fuel and the water. As the water enters the heat exchanger it absorbs heat from the combustion of fuel that has been ignited with a mixture of air.

The water enters cold, and leaves heated for use in heating spaces or domestic water purposes. The high temperature flue gas is exhausted out to the atmosphere through a vent. This is wasted heat and energy that you have paid for. If this boiler is 75% efficient, then basically you’ve exhaust 25% of your money out the flue. The condensing boiler makes use of this heated flue gas before its exhausted to the atmosphere.

How Condensing Boilers Work

How a Condensing Boiler Works by using two heat exchangers instead of one. This additional heat exchanger is used to capture the heat from the flue gases being exhausted. It’s called a condensing boiler becomes it removes latent heat (moisture) from the hot flue gas causing water to condense out of the flue exhaust air. This moisture collects at the bottom of the heat exchanger and must be drained to an approved drain receptor, much like you would with an air conditioners condensate drain. Since the heat exchanger is exposed to moisture it must be made of non-corrosive material, such as stainless steel.

Checkout these Condensing Boilers here

This condensate from the boiler must be treated before it is allowed into the drain system, because it’s considered acidic. This is accomplished by adding a little inline filter on the drain line. The filter may contain limestone which absorbs some of the acidic nature of the condensate, neutralizing it before it enters the drain.

The incoming cold water is preheated as it passes through the secondary heat exchanger before it enters the primary heat exchanger. This secondary heat exchanger is what increases the efficiency of the condensing boiler. The secondary heat exchanger gives the condensing boiler a second opportunity to absorb heat from the energy expended during combustion, by absorbing heat from the exiting flue gases. By capturing heat that would otherwise be wasted the condensing boiler achieves higher operating efficiencies.

These higher efficiencies are why condensing boiler are mandated in some jurisdictions, and why utilities often offer rebates. Check with your local utility company to see if rebates or incentives are available for changing a conventional boiler to a condensing boiler. Non-condensing or standard boilers have a range of efficiency from 75% to 84%, while condensing boilers can exceed 90% and all the way up to 98%. This will allow you to save on your annual fuel cost while also helping the environment.

Non-condensing Boiler vs Condensing Boiler

If you spend a dollar on fuel for your standard boiler at 75% efficiency, then you are throwing away 25% of your money through the heated exhaust gases. This is $0.25 cents for every dollar you spend. With a condensing boiler or heater that is 95% efficient, you are making your dollar more efficient as now only 5% is wasted in the exhausted flue gas. This means that for every dollar you spend, only $0.05 cents is wasted on flue gas exhaust.

Within the condensing boiler, the flue gas and water travel in opposite directions. The flue gas first enters the primary heat exchanger, while the water first enters the secondary heat exchanger.

Checkout these Condensing Boilers here

Flue Gas Material

Since a condensing boiler has much lower flue gas temperatures, most manufactures recommend the use of PVC or CPVC. Installing plastic piping is easier and less expensive than the standard metal flues used in conventional boilers.

For those of you who love the science behind the operation, just remember that the latent heat from the condensation provides around 970 Btu/Lb. of latent energy. This latent heat is what contributes to the increased efficiency, as this heat would otherwise be exhausted to the atmosphere. Boiler efficiency increases as the return water temperature decreases. Condensation occurs below 130F (54.4C), with the greatest efficiencies occurring the closer the return water gets to 60F (15.5C).

In commercial applications its best to get your supply temperature down to 140F (60C) as this provides an opportunity for better efficiencies. The engineer will have to make sure that the heat exchangers or whatever is receiving the heating hot water can operate at lower supply temperatures, as this will affect the surface areas of coils.

Considerations for Retrofitting a Non-condensing Boiler to a Condensing Boiler

Here are some main points to consider in commercial applications when retrofitting a project that has a conventional non-condensing boiler to a new condensing boiler.

Keep return water temperature as far below 130F (54.4C) as possible to take advantage of the increased efficiency at these lower temperatures.
Condensate drain piping with an inline filter to neutralize the acidic condensation. This includes the requirement for an approved drain receptor.
Boiler flue/stack to be installed using PVC or similar material
Heat Exchanger to be made of non-corrosive material, such as stainless.
Higher delta-T for existing fan coils or heat exchangers. Do they have the ability for lower flow (GPM) with greater temperature difference using a lower return temperature?
The old system might have been designed with a smaller Delta-T, maybe 20F (11C) (The difference between Supply & Return Water Temperatures). The new condensing boiler can run on a wider range of Delta-T, such as 30F to 50F (17C to 28C), allowing for lower GPM’s and pressure drops through heat exchangers. This saves on pump energy due to reduced flow and head.

Applications for using lower return water temperatures and a condensing boiler include, residential water heating and swimming pools, water-source heat pumps, hydronic radiant heating, snow-melt systems and geothermal.

How a Condensing Boiler Works

How Fan Coils Work in HVAC Systems

MEP Academy Instructor

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May 8, 2022

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How Fan Coils Work in HVAC Systems. In this article you’ll learn what a Fan Coil Unit (FCU) is, and where they’re mostly used in the commercial HVAC industry. We’ll cover the different types of fan coils, including 2-pipe, 4-pipe, horizontal and vertical.

If you prefer to watch the YouTube version of this presentation than scroll to the bottom for the video.

Fan Coil Components

Fan coils are very simple compared to other pieces of equipment. The fan coil contains a filter, fan, coil, and a drain pan to catch condensate from the cooling coil. The source of the heating and cooling is usually provided by a Chiller and Boiler located in a mechanical room, or outside on the roof.

Air enters the back of the fan coil and passes over filters before passing over the heating and cooling coils. The fan can be arranged in either a blow-through or draw-through configuration. With a blow through, the fan is before the coils, in a draw-through, the fan is after the coils.

The filters provide a means of keeping the air free of dust and particles, while preventing the coils from becoming clogged. The filter can be in a filter track attached at the back of the fan coil or a separate return air filter grill could be provided in the ceiling such as is common in some hotel room style installations using horizontal fan coils.

Depending on the size of the fan coil, there could be anywhere from one to three fans or more within the housing. These fans can be provided with ECM motors which make them energy efficient.

The fan coil will contain either one or two coils, depending on the design. There could be a heating and cooling coil installed, or just one coil for either heating or cooling. We are only discussing water-based fan coils, so refrigerant based DX coils are discussed in another article.

The cooling coil will require a drain pan to catch the water dripping off the coil. This is moisture that has been removed from the air and has condensed on the cold coil, much like you see condensate form on the outside of a glass of ice water. Its required to have drainpipe from this drain pan to an approved waste receptor, like a floor sink or the tailpipe of a sink.

How Vertical Fan Coils Work

Just like the vertical stacked Heat Pumps used in hotels, there are also Vertical Stacked Fan Coils. These vertically stacked fan coils can be either a two-pipe or four-pipe system. Using a 4-pipe system, there will be a chilled water and heating hot water supply and return piping, and of course a fifth pipe for condensate.

Vertical Stacked Fan Coil Unit FCU - High-Rise Hotel, Dorms, Apartments — Vertical Stacked Fan Coil Unit FCU – High-Rise Hotel, Dorms, Apartments

These vertical fan coils come with riser piping attached for easily stacking them one on top the other from floor to floor. These are best used in high-rise building such as hotels, condominiums, apartments, dormitories or similar high-rises.

Vertical Stacked Fan Coils in High-rise Hotel, Apartment or Dorm. (FCU)

Vertical fan coils are usually available from 3/4 ton to 4 Tons, or from 300 CFM to 1,600 CFM. The Chilled water entering temperature could range from 42F to 48F, with heating hot water entering temperatures of 120F to 180F. The units weight anywhere from 200 to 300 pounds.

How Horizontal Fan Coils Work in HVAC Systems

These Fan Coils use Chilled water or Heating Hot Water to provide the room with cooling or heating. A central ventilation unit will provide tempered air through a main duct to all the fan coils. This is the primary air supplied to the inlet of the fan coil to provide the required ventilation air (outside air) in accordance with ASHRAE 62.1. The fan coils reduce the amount of ductwork needed by the central system, because most of the heat transfer is done using water instead of air, by using Chilled Water or Heating Hot Water.

Horizontal 4-Pipe Fan Coil Units using a Chiller and Boiler

In the above image is a ducted return system where the supply air recirculates back into the fan coil. Some method of providing ventilation air will be required to meet code, which we’ll show shortly.

Fan coils provide both sensible and latent cooling, along with heating at the zone level, while the central ventilation unit conditions the outside air that feeds all zone fan coils.

Since the coils are very small in fan coil units, they’re not suited to handle large quantities of latent heat often brought in by ventilation or outside air. In these cases the use of a dedicated outside air system (DOAS) is recommended.

Fan coils can be either ducted or non-ducted and can be horizontal or vertical in configuration, and can be exposed or concealed.

Fan Coil Units with Dedicated Outside Air Systems (DOAS)

The benefit of using a DOAS is that the latent and sensible heat of the ventilation air can be handled by the Dedicated Outside Air System, while the fan coil will handle the load of the room it serves. This outdoor air can be decoupled from the fan coil units allowing any zones fan coil to be running at slow speed or be switched off when not in use, while still receiving ventilation air. Decoupled ventilation air means that the air from the outdoor air system is fed directly to the room without entering the fan coil unit, its totally independent of the FCU.

Horizontal Fan Coils with Dedicated Outside Air System

Fan coils are limited on their coil, fan and filter capacities. If the project requires additional heating or cooling capacity, then the use of a Blower Coil will provide the same benefits as a fan coil but with increased capacity. Blower coils come in larger CFM sizes, and higher static pressures, with coils that are larger and can provide additional heating or cooling capacity. These larger blower coils provide room for thicker filters, making for better filtration.

Horizontal Fan Coil with Chilled Water and Heating Hot Water Coils

Hope you enjoyed How Fan Coils Work in HVAC Systems, if you prefer to watch the video, see YouTube video below.

Learn How Fan Coils Work in HVAC Systems

How HVAC Heat Pumps Work

MEP Academy Instructor

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May 1, 2022

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We’ll cover How HVAC Heat Pumps Work, and the differences between an Air-Cooled and Water-Cooled Heat Pumps. We’ll explain the different styles of heat pumps used in residential and commercial buildings. You’ll learn the differences between air and water-cooled, packaged versus split systems, vertical versus horizontal, and ground and water source heat pumps.

If you prefer to watch the YouTube version of this presentation scroll to the bottom.

Refrigerant Cycle of a Heat Pump System – Reversing Valve

The Heat Pump has the same basic refrigeration circuit as a standard Air Conditioner except for a few specific components to help it succeed in both heating and cooling with the same refrigerant circuit. See our video on Refrigerant Circuits if you need a basic understanding on how they work. The main component that helps it function in both modes is the “Reversing Valve”.

Checkout these Heat Pumps here

Refrigerant Cycles - Standard Air Conditioner vs Heat Pump — Refrigerant Cycles – Standard Air Conditioner vs Heat Pump

The reversing valve has two modes of operation, its either in heating or cooling mode. The reversing valve provides changes in direction for the refrigerant flowing through the system, it reverses the flow, hence reversing valve. The reversing valve is the refrigerant traffic controller, changing the direction of refrigerant flow based on the demand of the space controller. The reversing valve sends the hot gas discharge from the compressor either to the outdoor unit heat exchanger or the indoor heat exchanger.

Reversing Valve in HVAC Heat Pump System

In relationship to the compressor, cooling is always accomplished on the suction side of the compressor, and heating is furnished on the discharge side. What the reversing valve does is switch the compressor discharge to go to the indoor coil when heating is required. It’s basically that simple, as the reversing valve acts as a traffic controller, sending refrigerant in one of two directions from the compressor.

To understand this better, we’ll walk through what happens in each season when heating or cooling is required.

Checkout these Heat Pumps here

Heating Mode

How HVAC Heat Pumps Work in Heating Mode. Starting at the compressor where the refrigerant is compressed causing the temperature and pressure of the refrigerant to increase. This high-pressure/high temperature gas (vapor) refrigerant will then enter the reversing valve where it will be directed to the indoor coil.

This high pressure, high temperature gas enters the indoor coil where cooler air from the space passes over the indoor coil absorbing some of the heat from the refrigerant, thereby heating the room, while causing the refrigerant gas to give up its heat and condense into a high-pressure liquid.

The refrigerant will than leave the indoor coil as a high-pressure liquid and enter the expansion valve where it’s pressure will be reduced causing it to become low-pressure liquid. See our video on expansion valves for more info.

This low-pressure liquid refrigerant will than enter the outdoor coil where it will absorb heat from the outdoors, causing the low-pressure liquid refrigerant in the outdoor coil to evaporate, absorbing the heat. This low-pressure refrigerant gas than enters the compressor where the cycle repeats itself.

Cooling Mode

How HVAC Heat Pumps Work in cooling mode, the heat pump acts the same as a standard air conditioners refrigerant cycle, whereby the condenser sends high pressure liquid to an expansion valve that lowers the pressure of the refrigerant going into the evaporator or indoor coil.

The heat from the space is passed over the indoor coil causing the refrigerant to boil or evaporate and absorb the heat from the air. This will cause the air to cool as its passes over the cold coil and head back to the space colder.

Checkout these Heat Pumps here

Packaged vs Split System Heat Pumps

You can get a Heat Pump that is all contained in one box, called a Packaged Heat Pump, or you can install it in two pieces which is called a split-system, and is commonly found in residential projects.

The split-system has an outdoor section, which houses the compressor and a heat exchanger with a fan in all air systems. The indoor section of a split system will have a heat exchanger and a fan. This is an all-air system, as each heat exchanger uses a fan. There are also water-sourced version which will cover now.

Water Source Heat Pumps

You’ll find the use of water source heat pumps in various sizes of commercial buildings. This allows for the use of a common water loop that works as a means of moving heat around. This heat can be discharged or absorbed from the water loop by the indoor heat pumps. The water loop is maintained between approximately 60 and 90 degrees. To help maintain the loop temperature within this temperature range a boiler is added to ensure enough heat is available during winter while the closed circuit cooling tower will reject additional heat during the summer or hot days.

The water is sent to a closed circuit cooling tower mounted outside on the ground or roof level. The water is in a closed loop, meaning that it never gets exposed to atmospheric elements. This keeps the heat exchangers of the water-cooled heat pumps clean by preventing impurities entering from exposed water sources.

With water-source heat pumps, heat rejection or absorption into the heat exchanger is through water. In an air-cooled system, a fan is used for heat transfer.

There are two commonly used types in the commercial industry, vertical and horizontal water source heat pumps, in addition to water source heat pumps used in ground source systems discussed later.

Vertically Stacked Water Source Heat Pumps

How HVAC Heat Pumps Work using vertically stacked units. There are lots of high-rise hotels that use vertically stacked water sourced heat pumps to provide heating or cooling to their guest-rooms. They are hidden behind the walls with a supply and return grill mounted to the face of the unit, and a temperature sensor nearby.

A vertically stacked water-source heat pump uses a closed-loop of water as a means of heat transfer. When in cooling mode the unit will reject its heat to the water loop, and while in heating mode it will absorb heat from the loop. The vertical heat pumps range in tonnage from 1/2 to 3 tons.

Vertical water source heat pumps contain the complete refrigerant circuit, with compressor, two heat exchangers, reversing valve and expansion valves.

Horizontal Water Source Heat Pumps

Various commercial buildings will have concealed horizontal water source heat pumps installed for each zone or room. These may also be found in hotel guestrooms, usually mounted above the entrance or bathroom with a stub of duct to feed a supply grille, with a ceiling mounted return grill. The return grill could also contain a filter.

These units are also available for exposed locations, usually near an exterior wall to provide a method for fresh air. Just like the vertical stacked heat pumps, these horizontal heat pumps will have a closed circuit cooling tower mounted outside.

Ground Source Heat Pumps

The sun shining on the ground provides for heat energy to be stored in the soil. This underground stored energy can be used with ground source heat pumps. With ground source heat pumps the ground is used as a means of absorbing heat or providing heat.

A pump circulates water through piping buried in the ground. This piping is connected to a heat exchanger in the heat pump where the heat from the ground will be absorbed or rejected into the refrigerant circuit.

Ground Water Source Heat Pumps

Bodies of water, like lakes or ground water can also be used as a source of energy. They use heat exchangers as a means of separating the refrigerant from the water. Water is mixed with antifreeze like glycol in some climates to avoid freezing and is pumped through a maze of hoses buried in the ground. The water circulates around the buried piping and then back to the heat exchanger where it transfers or absorbs heat from the refrigerant.

Ground - Water Source Heat Pump - Open Loop — Ground – Water Source Heat Pump (Open Loop)

When using groundwater, there are two types, the open loop which is shown here, and a closed loop version. The open loop system uses a pump to withdraw water from a lake or underground aquifer and send it through the heat exchanger where it will absorb or reject heat into the refrigerant before being sent back into the body of water.

In a closed loop system everything happens the same except the piping is closed and circulates the same water and antifreeze mix.

Water sources can provide a method of passive cooling, whereby the compressor can be shutoff.

Checkout these Heat Pumps here

How HVAC Heat Pumps Work in Residential and Commercial Buildings

How to Calculate Sensible and Latent Heat Transfer for Air

MEP Academy Instructor

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April 25, 2022

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How to Calculate Sensible and Latent Heat Transfer for Air

In this article we’re going to look at the Sensible and Latent Heat Transfer Equation for Air. This is useful when trying to determine either of the three variables, Btu’s, CFM or Delta in Enthalpy. When you know two of these values you can determine the remaining missing value.

If you prefer to watch the YouTube Video of this presentation than scroll to the bottom.

Sensible and Latent Heat Transfer Equation for Air

q = m ∆h

q = CFM x 0.075 lb/ft²x 60 min/hour x ∆h

q = CFM x 4.5 x ∆h

CFM is ft³/minute

M is the overall mass flow rate of air

h is the Enthalpy (Btu/lb.)

We’ll need to look at a Psychrometric Chart to gather the information needed for this calculation. This is also easily done using software, but it’s best to know how the software arrives at these values.

We’ll begin by calculating for the BTU’s when given the CFM, and the temperature and relative humidity of the Entering and Leaving Air conditions. Remember we’re dealing with both sensible and latent heat. That means were dealing with two factors, the sensible or change in temperature and the latent, the change in state, in this case it will be moisture condensing on a cooling coil.

Sensible and Latent Heat Transfer Formula for Air

Looking at this chilled water coil we see that there is 2,000 Cubic Feet per minute of air flowing through this coil and the temperature of the Entering air is 90°F and 40% relative humidity with the Leaving Air at 55°F and 100% relative humidity.

Example:

2,000 CFM of outdoor air (Ventilation Air) at 90°F and 40% relative humidity (RH) is drawn through a cooling coil that brings the conditions to 55°F and 100% relative humidity (RH)

Step #1 – Plot the given conditions on the Psychrometric Chart

Step #2 – Get the h1 and h2 values from the Psychrometric Chart 34.9 and 23.2

Step #3 – Enter all values into equation.

q = CFM x 4.5 x ∆h

q = 2,000 x 4.5 x 11.7 = 105,300 Btu/hour

With this information we can solve for how many btu’s are being supplied to the air.

Step one is to plot the entering and leaving air conditions on a psychrometric chart to determine the enthalpy. For the entering air conditions of 90°F and 40% relative humidity (RH), we enter here along the horizontal part of the chart that reflects temperature and then we go vertical straight up from there until we hit our 40% Relative Humidity line and then diagonally to the left until we intersect the enthalpy line. Here we get we get an enthalpy of 34.9, and then we plot the leaving air conditions of 55°F and 100% relative humidity we get an enthalpy of 23.2. 34.9 – 23.2 gives us an enthalpy of 11.7 Btu/lb.

Sensible and Latent Heat of Air Plotted on Psychrometric Chart

Step two is to put all the known values into our formula and make the calculation.

We have our formula of q = CFM x 4.5 x ∆h

Now we enter our values, we get

q = 2,000 x 4.5 x 11.7 = 105,300 Btu/hour

Now we quickly explain where the value of 4.5 in the calculation is derived from. First, we have the weight of Air at 0.075 pounds per Ft3, then we have the conversion of 60 minutes into hours. This is what that looks like

0.075 lb/ft³ x 60 min/hour = 4.5

With all these units, we can see which units of value remain by crossing out those that are eliminated in the formula as such

q = 2,000 ~~Ft3~~/~~minute~~ x 0.075 lb/~~ft³~~ x 60 ~~min~~/hour x 11.7 Btu/lb = 105,300 Btu/hour

how to Calculate the Sensible and Latent Heat Transfer of Air

Checkout these similar Videos related to sensible heat:

Sensible Heat Transfer Formula for Air

Sensible Heat Transfer Formula for Water

How Standard Boilers Work

How Condensing Boilers Work

Flue Gas Material

Considerations for Retrofitting a Non-condensing Boiler to a Condensing Boiler

Fan Coil Components

How Vertical Fan Coils Work

How Horizontal Fan Coils Work in HVAC Systems

Fan Coil Units with Dedicated Outside Air Systems (DOAS)

Refrigerant Cycle of a Heat Pump System – Reversing Valve

Heating Mode

Cooling Mode

Packaged vs Split System Heat Pumps

Water Source Heat Pumps

Vertically Stacked Water Source Heat Pumps

Horizontal Water Source Heat Pumps

Ground Source Heat Pumps

Ground Water Source Heat Pumps

Sensible and Latent Heat Transfer Equation for Air

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