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Wednesday, February 26, 2025
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How do Geothermal Heat Pumps work

MEP Academy Instructor
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How do Geothermal Heat Pumps work

How do Geothermal Heat Pumps work? We’ll learn the different types of Geothermal Heat Pump Systems, along with information on where to find incentives and rebates, the efficiency compared to a regular heat pump and the cost you might expect to pay to have one installed.

If you prefer to watch the video version of this presentation than scroll to the bottom or click the link here “How do Geothermal Heat Pumps work?“

Ground Source Heat Pumps - Ground Temperatures and Loop Depth
Ground Source Heat Pumps – Ground Temperatures and Loop Depth

The use of geothermal heat pump systems takes advantage of the earths relatively constant temperature beneath the surface based on location and height. The earth maintains a ground temperature range from 45°F (7°C) to 75°F (21°C). taking advantage of this natural heat source is what gives the Geothermal Heat Pump greater efficiencies than a standard heat pump. This source of heat is also naturally renewable making it a great energy source.

The Geothermal Heat Pump System comes with various options on how to tap into this natural reservoir of heat. We will discuss open and closed loop systems, and horizontal versus vertical system, and when to use them.

Checkout these Geothermal Heat Pump here

The cost of a geothermal heat pump system is more than that of a typical heat pump system, but this cost is saved by possible incentives and rebates in addition to the yearly energy savings which we’ll cover shortly.

Geothermal Heat Pump System in Cooling Mode
Geothermal Heat Pump System in Cooling Mode

Geothermal Heat Pump in Cooling mode

In cooling mode, warm air from within the building is brought into the ground source heat pump. The heat pumps indoor coil will absorb the warm air into the cooler liquid refrigerant circulating through the coil. Absorbing the heat will cause the refrigerant to boil and turn into a gas. The refrigerant will circulate through the system and be absorbed by the cooler water circulating through the system from the underground.

The heat is then absorbed by the water and circulated underground where the heat is rejected to the cooler ground. Remember the 2nd law of thermodynamics states that heat moves from a warmer to a cooler item. The water and refrigerant never come in contact with each other. For a complete understanding of the refrigerant cycle see our other video.

Geothermal Heat Pump System in Heating mode
Geothermal Heat Pump System in Heating mode

Geothermal Heat Pump in Heating mode

In heating mode the opposite occurs. We will always follow the heat as stated by the second law of thermodynamics. The heat in this case is provided by the ground. The cool water is circulated to the ground where it absorbs heat from the ground.

This warm water then circulates into the ground source heat pump where it is absorbed into the refrigerant causing the liquid refrigerant to boil and turn into a vapor. The hot refrigerant is then circulated to the indoor coil where it comes in contact with the cooler return air from the space. The cool return air absorbs the heat from the hot refrigerant and heats the leaving supply air.

Checkout these Geothermal Heat Pump here

Types of Geothermal Heat Pump Systems

In order to tap into the earths free source of energy we’ll need to run plastic tubing beneath the surface. This tubing acts as a heat exchanger between the fluid in the tubes and the ground. The tubing is configured in various patterns and depths based on available land area and the composition of the soil below ground.

If there is enough ground area and the soil is good for heat transfer than a horizontal system can be installed. If there isn’t enough ground area or the soil isn’t good for heat transfer, then vertical tubing is another option. These systems circulate water with antifreeze or there is the option to use a refrigerant based system. Another option if you have a body of water nearby is to use an open or closed loop system into the body of water. We’ll cover each of these now.

Horizontal loop GSHP

Given enough area for the tubing to achieve the heat transfer required to support the cooling and heating load of the building or home, using the horizontal loop is more feasible than drilling vertically. Horizontal loops are buried from 3 to 5 feet (0.9 to 1.5m) deep and are economically feasible as long as excavation can be done without difficulty due to soil composition.

Geothermal Heat Pump Horizontal Trench with Looped Tubing
Geothermal Heat Pump Horizontal Trench with Looped Tubing

The length of the loop is determined by the amount of heat transferred required or the tonnage of the heat pump. In order to determine the length of tubing required, a heating and cooling load calculation is performed on the building. Tube length can run between 500 to 600 feet (152 to 182m) per ton of heat pump capacity. This means that a 4-ton system would require 2,000 to 2,400 feet (610 to 732m) of tubing. Allowing for spacing to achieve efficient heat transfer, an approximate area from 1/4 to 3/4 acre could be required for a typical sized home.

Vertical Loop GSHP

Using vertical loops requires less land area as the tubing is sent hundreds of feet below the surface. For commercial buildings this could include bore holes 100 to 500 feet (30 to 152m) deep, spaced 20 feet (6m) apart to allow for proper heat transfer. These holes can be up to 4” to 6” (10 to 15cm) in diameter and contain plastic tubing that traverses to the bottom where it makes a U-turn and comes back out of the hole where it connects to a horizontal manifold. Residential systems would require fewer bores and would most likely be 300 feet (91m) deep or less. Vertical loops can be used when there isn’t enough land area and when greater efficiency maybe required.

The Slinky Geothermal Loop Installation

This geothermal System uses coiled tubing which allows for the use of less area by increasing the heat transfer ability per area used. This occurs because the tubing is coiled in the trench requiring less land area, but more tubing per linear feet. The coils are laid in a horizontal trench 3 to 8 feet (1 to 2.4M) deep. A combination of water and antifreeze circulate through the tubing and the heat pumps heat exchanger.

Geothermal Heat Pump Loop
Geothermal Heat Pump Loop

DX Refrigerant Based Geothermal Ground Loop

Another energy efficient option is the DX ground loop system that uses refrigerant circulating around a buried copper coil. Instead of water, refrigerant is the heat transfer medium, avoiding the additional step of transferring the heat to the refrigerant in a water based system. This helps with the increased efficiency and greater heating capacities. This also eliminates the need for a water pump, as this is a waterless system.

Another difference is that this loop is in a wide vertical hole, something like 3 feet (1m) in diameter and 70 feet (21m) deep. This eliminates the need for large areas of land. The soil will need to be tested to make sure it’s not corrosive to the copper, and if found to be corrosive then a ground loop protection method will be installed. 

Checkout these Geothermal Heat Pump here

Ponds, Lakes or Water Based Sources

Having a body of water near the property allows for the option of using water as the heat sink, where heat is transferred to and from the tubing either in an open or closed loop arrangement.  

Ground Source Heat Pump - Closed and Open Loop Systems
Ground Source Heat Pump – Closed and Open Loop Systems

Closed loop Systems.

The tubing can be installed at the bottom of a pond on the property if the pond is large enough, maybe 1/2 an acre or larger depending on its depth. If close enough to a lake this option is also available pending local authority approval. A pump circulates the water and antifreeze solution through tubing within the body of water where it rejects or absorbs heat from the geothermal heat pump.

The use of lakes, wells, ponds or waterways for a heat sink.
The use of lakes, wells, ponds or waterways for a heat sink.

Open Loop System

The difference between the closed and open loop systems is that the open system uses the pond, well or lake water to be circulated through the tubing and up to the heat pump. This raises additional concerns for environmentalist and code authorities about water depletion and ground water contamination.

The use of well water is an option if a body of water exist under your property and the use of a horizontal ground loop doesn’t work for lack of area or feasibility. Open loop systems require more maintenance than a closed loop, due to the minerals and other impurities that maybe in the water. 

Are open loop Systems Legal?

There are laws governing the use of bodies of water for the use of any open system that will take water from the source and use it in some process before returning it back again. The legitimate concern is what happens to the quality of the water in the process. Another concern is for the wild life or living organism in the water that maybe effected by the warmer discharge temperatures.

You’ll need to check with the jurisdictional authority when contemplating the use of any body of water. An alternative would be a closed loop system which should be less stringent.

Is a Geothermal Heat Pump System worth the Cost?

Energy savings from the installation of a geothermal heat pump system could take anywhere from 5 to 10 years to payback the additional investment cost above a conventional system according to the department of energy.

The DOE states that an average geothermal heat pump system costs about $2,500 per ton of capacity. If a home requires a 3-ton unit, then it would cost about $7,500 (plus installation and drilling costs). A comparable Air Source Heat Pump system with air conditioning would cost about $4,000, but the energy costs could easily equate to the extra cost of installing a geothermal heat pump.

Geothermal heat pump systems have an average 20+ year life expectancy for the heat pump itself and 25 to 50 years for the underground infrastructure. 

Geothermal Heat Pump System Frequently Asked Questions (FAQ)

1) How Long Do Geothermal Loops Last?

The geothermal loop is buried underground so it’s protected well and should last anywhere from 50 to 100 years. The underground piping often has a warranty period of 25 to 50 years, check with the manufacture about their warranty period.

2) How long does it take for a Geothermal System to Pay For Itself? 

Based on the type and size of the project the payback period varies but expect 4 years or more. Ask your contractor for a payback analysis.

3) Do Geothermal Systems use a lot of Energy?

No. Geothermal systems are used for the purpose of saving energy and providing a more sustainable solution. The heat pump uses electricity but more efficiently.

4) Do Geothermal System Require A lot of Maintenance?

No. Geothermal systems require less maintenance than other types of heat pumps. 

5) How Deep Should Geothermal Horizontal Loops be?

Anywhere from 3 to 8 feet (1 to 2.4m) deep is a common depth for a horizontal geothermal heat pump system. The tubing can be placed side by side in a couple feet wide trench, or spaced several feet apart at different depths in a more shallow trench.

6) What is better,  a Closed or open loop Geothermal System?

A open loop system will be more efficient and less costly, but will be more regulated due to the system discharging into the water way.

7) Can I Install my Own Geothermal System?

The installation is best done by an experienced contractor and is not something a home owner should attempt on their own.

8) Do you need supplemental Heat when using a Geothermal Heat Pump?

A properly sized Geothermal heat Pump should be sufficient to handle the calculated heating and cooling load of a space. This is why it’s important that a load calculation be done to ensure that the system is sized correctly. If need be, additional electric heat can come on after its maxed its capacity

9) Is a Geothermal System worth the investment cost?

One of the greatest benefits of a geothermal system is that they use 25 % to 50% less electricity than your typical heating and cooling system. And efficiencies can be increased by adding a desuperheater that heats the domestic water. If you consider the environment then the investment value is increased as less carbon is injected into the environment.

10) What material is used for geothermal heat pump underground tubing?

The three most commonly used materials for water based systems include PEX (polyethylene), HDPE (high-density polyethylene) and PE-RT (polyethylene (PE) resin).

11) Can my Geothermal Heat Pump be powered by a Solar System?

A PV Solar system can provide the power needed to run a geothermal heat pump. Have your contractor do a comparative analysis between the capacity of the solar system and the required power of the heat pump system.

12) How much does a Geothermal System Cost?

Cost vary by location and type of system installed. Residential systems can range from $25,000 on the low end for a small system to over $60,000 for larger systems. For commercial properties the range is much greater because the system sizes encountered are much larger than residential systems.

13) What size tubing is used for Geothermal Heat Pump Systems?

The loops are typically using 3/4” to 1” (1.9 to 2.54cm) tubing, while the main headers will be larger in the range of 1-1/2” (3.8cm) for a 3-ton system.

14) Are there any Tax Rebates or Incentives for Geothermal Heat Pump Systems?

In 2022 tax credits were extended through 2034 for ENERGY STAR rated geothermal systems. Check local utility companies for incentives and geothermal Heat Pump manufactures for rebates.

Geothermal Heat Pump Process

One of the first things when considering the installation of a geothermal heat Pump system is to engage an experienced contractor. The contractor should develop a plan for the execution of the system starting with the options on the type of Geothermal System appropriate for your site. This should include a site visit from the contractor and a review of the home or space. A heating and cooling load will need to be done on the home to determine the correct size of the system.

Included in the contractors review should be an analysis of the energy savings from the various heat pump systems, including any possible rebates, incentives or tax credits. 

How do Geothermal Heat Pumps Work

How do Evaporative Coolers Work

MEP Academy Instructor
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How do Evaporative Coolers Work

How do Evaporative Coolers Work? Areas with low-humidity levels can benefit from evaporating water into the air supplied for space cooling, whether residential or commercial. There are two basic types of evaporative coolers, indirect and direct evaporative coolers. We’ll be covering direct evaporative coolers, often called swamp coolers, which means that the water used for cooling comes in direct contact with the air stream.

We’ll show you how they work and how they are installed. We’ll also learn how to size an evaporative cooler based on climate zones, along with air flow strategies and how they’re ducted. 

If you prefer to watch the Video of this presentation, then scroll to the bottom or click on the following link “How do Evaporative Coolers Work“.

Evaporative cooling involves passing dry outdoor air over water saturated pads which causes the water to evaporate and cool the air delivered to the space. 

Swamp Cooler - Direct Evaporative Cooler
Swamp Cooler – Direct Evaporative Cooler

Construction of an Evaporative Cooler

The evaporative cooler is housed in a sheet metal box. Inside the box there is a fan that blows air into the space, and a water reservoir where a recirculating water pump will sit. Then there is tubing from the pump to spray heads above media pads on the air intake sides of the cooler. There is a float valve and float to maintain water in the reservoir, while an overflow drain is provided for excess water drainage. 

There are several options on where to install the evaporative cooler. It can be installed on the roof, a wall or on the ground. 

Checkout these Evaporative Coolers here
Evaporative Cooler or Swamp Cooler Construction
Evaporative Cooler or Swamp Cooler Construction

Roof Mounted Evaporative Cooler

We’ll explain a roof mounted system as it has more steps. After the system has been sized and selected, a hole would be cut in the pitched roof between roof supports for the supply air duct, making sure to seal tightly around the perimeter of the penetration with flashing to avoid leaks. The best location is on the backside of the home to avoid visibility from the front.

Next, you would use a crane or other method to safety hoist the evaporative cooler onto the roof positioned over the duct opening so that it lines up with the evaporative coolers bottom opening. Install support legs to add stability. 

Evaporative Cooler Electrical

You will need to install a 120-volt electrical outlet near the unit and run wire inside to a wall switch or a controller. Check your local code as you may also forgo the electrical outlet and just run the electrical conduit and wire directly to the switch from the cooler. The controller will allow for low and high speeds, and for a fan only option. There may also be a pump only option that allows you to give time for the pads to absorb the water before sending hot air over them. Again, you’ll need to have a roof jack where the electrical conduit penetrates the roof. This will ensure that you can make a proper seal to avoid roof leaks.

Evaporative Cooler Water Tubing

A small residential system could use a 1/4” water tube. The tubing will need to be connected to an existing water pipe to provide the cooler with a continuous supply of water. The tubing can be installed in copper, PEX or plastic tubing, check your local code to make sure of the approved material types. It’s best to have one continuous length of tubing in the attic or in concealed spaces to avoid additional points where leaks could occur. 

A shutoff valve should be provided at the point of connection to the main water supply to isolate the tubing if there is a leak, and at the evaporative cooler for quick access. In areas that experience freezing winters, it’s a good idea to provide a tee connection near the main water source with a drain valve to drain the tubing to avoid freezing, which could cause damage to the tubing. 

Checkout these Evaporative Coolers here

The tubing connects near the evaporative coolers float valve. This tubing will also need a roof jack to prevent roof leaks. There will also need to be a connection for the overflow drain connection as you don’t want unsightly water stains running down your roof.

Evaporative Cooler Ductwork

There are several options when installing the supply air duct. There is the option to have one large opening in a central location like the hallway, hopefully the evaporative cooler can be located directly above and make a simple straight duct drop. 

Roof-Mounted Direct Evaporative Cooler
Roof-Mounted Direct Evaporative Cooler

You could also duct the supply air to each room. 

Direct Evaporative Cooler ducted to multiple Rooms
Direct evaporative Cooler ducted to multiple Rooms

Frame out around the ceiling opening and install a supply grille. You should never use the existing air conditioning ducts as they aren’t sized for the air volume of an evaporative cooler. 

Selecting an Evaporative Cooler

Evaporative coolers are rated by the volume of air that they can provide in cubic feet per minute (CFM). Manufactures recommend that a certain number of air changes be provided depending on the geographical location of the space. For an explanation on how to calculate Air Changes per Hour, see our video on “How to Calculate Air Changes per Hour”. The warmer the climate the greater the number of air changes that will be required. 

Air changes could range from 20 to over 40 air changes per hour. For a 1,500 Ft2 home with 8-foot ceilings this would roughly be about 4,000 CFM at 20 Air Changes per hour, or 8,000 cfm at 40 Air changes per hour. Evaporative coolers use larger volumes of air than a traditional air conditioner, so the ductwork is larger to handle the greater CFM’s. 

Evaporative Cooler Sizing Chart
Evaporative Cooler Sizing Chart

Pacific Gas and Electric (PG&E) has a chart for sizing Energy-Efficient Ducted Evaporative Coolers for properties located in hot, dry climates (such as California Energy Commission (CEC) climate zones 11, 12 or 13, the Central Valley) and if your home was 1,250 Ft2, this would require a 5,000 CFM unit. This equals 4 CFM/Ft2. These values are based on 8-foot ceilings.

You can see that in the zones with an Average Climate a design of 3 CFM/Ft2 was used, while a Hot dry Climate is designed using 4 CFM/Ft2

Consult with an evaporative cooler supplier for the correct size for your application.

Airflow Strategies

Do evaporative coolers need to be vented? Yes, there should be a path provided for the large volume of air that is coming into the building. The air must go somewhere, so its imperative that you control the path of air to achieve the cooling results you’re looking for.

There are several strategies for providing proper airflow within the building served by an evaporative cooler. 

Vents can be provided in the ceiling that allow hot air to escape the rooms as the new cooler air enters. These ceiling vents would exhaust into the attic space, thereby requiring the attic to be vented.

Evaporative Cooler Exhaust Vent Openings - Using Attic Vents
Evaporative Cooler Exhaust Vent Openings – Using Attic Vents

Venting into the attic also helps reduce attic temperatures which contributes to the overall objective of a cooler occupied space. Venting eliminates the security risk of having to leave the windows and doors open as used in the next strategy. 

Leaving the windows slightly open allows the warmer air to escape the room as the evaporative cooler brings in 100% outdoor air. There is no recirculation of air through the system, as there is with an air conditioning system.

Checkout these Evaporative Coolers here
Evaporative Cooler Air Strategies - Leaving Windows Open to Control Air Flow
Evaporative Cooler Air Strategies – Leaving Windows Open to Control Air Flow

With evaporative cooling it’s important to allow warm air to escape. This will help remove the heat from the space and avoid excessive moisture from accumulating in the building. Traditional air conditioners recirculate the air within the space and work best with all windows closed and a tightly sealed structure.

To control the flow of air within a home, it is recommended to strategically open certain windows to direct air movement. Avoid opening windows on the windward side, to avoid additional hot air from entering the space. Cracking open the windows on the leeward side of the building will allow for the warm air to escape. Avoid opening them too wide as hot air will enter the space, while not opening them wide enough will cause moisture to buildup in the space. Experiment with various openings to see how the air flows, while keeping windows closed in unoccupied rooms.

How Evaporative Coolers Work

The pump that is sitting in the water reservoir pulls water in and then sprays it over the media pads located on the side panels of the cooler, while the fan draws in hot dry air over the wet pads. The pump keeps the pads wet as the warm air travels through them, causing water to evaporative. 

When water evaporates and turns into a gas it cools the dry air entering the cooler. As water evaporates and the water level in the pan begins to drop, it will activate the float valve, which will allow water into the pan until the float valve shuts off the makeup water. 

The controller can be used to increase the fan speed on hot days from low to high, and or on mild days to fan only. A thermostat can be used to automatically turn the cooler on when a certain temperature is reached within the space, or a manually operated controller could be used. The thermostat can also start the water pump before the fan to ensure the pads are wet before hot dry air is brought in over them.

Evaporative coolers usually allow for several fan speeds and a fan only option. It should allow the water pump to be shutoff and only the fan to run to circulate air. Without the pump running, no water will be sprayed over the pads and the air will not be humidified. This works in mild weather or at night when less cooling is required.  The fan only option allows for its use like a whole-house fan.

The evaporative cooler uses water for cooling while the traditional air conditioner uses refrigerant. 

Remember that heat moves from a warmer substance to a cooler one, so the warm air is cooled down while the water absorbs some of the air’s heat, causing some of the water to evaporate. This drives the dry bulb temperature of the incoming air down, while increasing the wet bulb temperature and humidity level of the air entering the room.

As the heat from the air is absorbed by the water the sensible temperature of the air is lowered while its latent heat content or moisture level is increased. This raises the relative humidity of the space as this air is directly ducted into the space to be cooled.

Each side of a roof mounted evaporative cooler should easily have removal side panels for ease of media replacement.

Checkout these Evaporative Coolers here

Evaporative Coolers vs Air Conditioning

Evaporative coolers are much less expensive to purchase and operate than the convention air conditioner, as there is no compressor or condenser fan. The evaporative cooler uses just a fan and small water circulating pump. Since water is the basis of the cooling effect, they work best in low humidity areas.

Evaporative coolers are used for temperature reduction and humidification. There are two basic configurations, direct and indirect evaporative cooling. With a direct evaporative cooler, the air comes in direct contact with the water, as opposed to the indirect evaporative cooler where the water and air stream don’t meet each other.

With evaporative coolers there is less energy consumed then a traditional air conditioner, as the evaporative cooler only has a pump and fan that consumes energy. There is the use of water that needs to be considered. 

With the use of direct evaporative cooling the water meets the air provided to the space, giving the air a filtering effect. The washing of the air can remove dust, smoke, and particles from the air stream, much like a scrubber.

When using wetted surfaces or evaporative media pads, they should be made of materials that will prevent corrosion. The use of aluminum or stainless-steel helps prevent corrosion.

Where do Evaporative Cooler Work Best

Evaporative coolers work best in dry, low wet bulb, and low relative humidity areas, as the results of the cooling effect are the based on the difference between the dry bulb and wet bulb of the entering air. The dry bub temperature can’t be reduced lower than the wet bulb temperature, so this limits the amount of cooling. 

When the dry bulb temperature reaches the wet bulb temperature, the air is totally saturated with moisture. In high humidity climates evaporative coolers don’t work as well because they use evaporation as the process for cooling. Evaporation works best in low humidity regions. High humidity regions should use traditional air conditioners.

How do Evaporative Coolers Work

How Gas Furnaces Work

MEP Academy Instructor
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How Gas Furnaces Work

How Gas Furnaces Work. In this presentation we’ll cover how a furnace works and explain the various components, including the different types of furnaces that are used mostly in residential spaces, but also used in various commercial applications. Natural gas is the mostly used fuel for furnaces. We’ll explain the difference between a condensing furnace and a non-condensing furnace. We’ll discuss how furnaces are rated for energy efficiency and the type of flues used for each type of furnace.

If you prefer to watch the video of this presentation, then scroll to the bottom or click this link. How Gas Furnaces Work

How Gas Furnaces Work. Here is a vertical Gas Furnace with bottom return air.
How Gas Furnaces Work. Here is a vertical Gas Furnace with bottom return air.

Construction of a Furnace

The furnace can be installed vertically or horizontally in a closet, basement, attic, crawl space or equipment room. 

Checkout these Gas Furnaces here

The furnace is housed in a sheet metal casing. The latest models use a variable speed fan to blow air over the heat exchanger. These types of fans have direct drive ECM motors that are much quitter and run more efficient than traditional fans. The fans don’t handle a lot of static pressure, often a maximum of 1” W.C. (0.249 kPa). Warning “Installation and Service should be performed by a qualified installer, service agency or the gas supplier”.

Gas piping will be installed from the gas meter, or from a branch off the main gas line, and connect to an internal Gas Valve and manifold in the furnace. A gas shutoff valve should be provided at the furnace for isolation of the gas. The shutoff valve needs to be in a visible location close to the furnace for ease of use in an emergency or for maintenance. Between the shutoff valve and the furnace should be a union and drip leg. The union provides for the gas piping to be removed from the furnace if required.

Gas Furnaces - Vertical and Horizontal Furnaces
Gas Furnaces – Vertical and Horizontal Furnaces

A Drip leg should be installed to trap any condensate in the gas piping and prevent it from entering the furnace. The drip leg should be located away from where it could freeze. After the piping is installed, it will need to be pressure tested to ensure there are no leaks. The pressure test can be done using compressed air or an inert gas like nitrogen. Never use oxygen to pressure test gas piping. The use of an electronic leak detector can help identify any leaks indicated by a failed pressure test. Obviously, a flame would never be used to find a leak.

Pipe size depends on the volume of gas required and the size of the furnace, but for a small residential unit the gas piping might be just a 1/2”(20mm) pipe. The gas valve controls or modulates the flow of gas to the burners. The burners convert the fuel and air into heat that enters the heat exchanger. 

Furnace Heat Exchangers

With a condensing furnace there will be two heat exchangers, a primary and secondary heat exchanger. With non-condensing furnaces there is only one heat exchanger. The heat exchanger is where the room air absorbs heat from the burning fuel. By having two heat exchangers, the condensing furnace allows for additional heat transfer and lower flue gas temperatures. The secondary heat exchanger will most likely be made of stainless steel to prevent corrosion as condensate will occur at lower flue gas temperature. 

Checkout these Gas Furnaces here

Combustion Air

The combustion air will go up through the heat exchanger and to the outdoors, while the blower fan sucks in return air and blows it through the heat exchanger, then out to the spaces to be heated. The air delivered to the spaces and the burning fuel with its combustion gases are on opposite sides of the heat exchanger wall and never encounter each other. Some manufactures provide removability of the heat exchanger for easy serviceability. 

Gas Furnace
Gas Furnace

Combustion and flue exhaust will need to be provided. With a condensing furnace this is accomplished by installing a combustion inlet pipe to the outside (direct venting) or inside (non-direct venting), and a combustion flue exhaust to the outside. If using a condensing furnace, then vents can use 2” to 4” PVC as the flue gas temperatures are much lower on these types of furnaces. For non-condensing atmospheric furnaces its common to use “B” vent, check the furnace manufacture and local code authority for venting requirements.

There will be a direct spark ignition or hot surface ignition system for the lighting of the gas when heating is called for. Along with the direct spark ignition is a remote sensor that confirms that the gas is burning. This is a safety device to prevent gas from being released if no flame is sensed.

Condensate from Condensing Furnace

A condensate pipe will need to be installed for any condensing furnace installed. Condensing furnaces are more efficient, but the byproduct is condensate that needs to be routed to a drain. The drain will have to run through a neutralizing filter because of the acidic nature of the condensate. This neutralizing kit can be provided by the manufacture or bought separately.

Condensing Furnace - Condensate Neutralization Kit
Condensing Furnace – Condensate Neutralization Kit

Newer models will have integrated circuit control boards that could contain dip switches for easy setup adjustments.

Electrical

Electrical conduit and wire will be run from the breaker panel to the furnace. These furnaces require only 115 volts, single phase power to the unit. Inside the unit should be a transformer that reduces the 115 volts down to a lower control voltage.

There will be a safety switch on the cabinet door leading to the blower, so that when the door is opened the blower is shutoff. This prevents someone from getting injured from a moving fan wheel and motor during service.

Filters

Filters can be provided on the bottom or side inlet to the fan housing by adding a filter rack if one isn’t provided. Remember that the furnace should never be run without a clean filter in place. See our video on “Air Filters and Filter Housing Basics” to understand filters and how they’re rated.

Smart Thermostat

Look for furnaces that have some form of communication with a smart thermostat to provide system information and alerts to system problems. There are also mobile apps that allow for notification and setting adjustment remotely, including routine maintenance alerts. The thermostat should allow for modulation of capacity. There will be a control wire access port for the thermostat wiring coming from the conditioned space.

Smart Thermostats
Smart Thermostats

When the thermostat sends a signal to the furnace to provide heat, the combustion air fan will start to ensure proper air for the combustion of the gas. Then to confirm that the combustion fan is running there is some form of pressure switch that picks up pressure created by the fan which then energizes the hot surface igniter. After a preset time, the hot surface ignitor will allow gas to flow to the burners. After another preset time that the burners are operating, the blower fan will start and blow air out of the furnace into the space. If the system fails to lite the burners after various attempts, then shutoff the system and contact a service company to determine why. 

Thermostats often allow for two settings. One is auto, which lets the system cycle on and off to meet demand. The other is fan only, with this setting only the fan runs continuously without any heating. 

If adding a split system air conditioning unit to the installation, the DX coil will mount on the discharge of the furnace and share the same fan for air flow. 

The furnace can weight from 100 to 200 pounds depending on the heating capacity of the unit.

Upflow Furnaces

With up flow, vertical furnaces, the Return air will enter the bottom of the furnace or side, and travel through a filter before entering the fan section where the air is blown through the burner and then the heat exchanger. As the air leaves the furnace it enters a plenum and then through distribution ductwork to deliver the heated air to each room.

Downflow Furnaces

Some buildings use the crawl space for the distribution ductwork and a furnace that provides a downflow configuration. The return air enters the top of the furnace with the supply air exiting at the bottom. 

Horizontal Furnaces

When using a horizontal furnace, they can be installed in attics, crawl spaces or an open space. When the furnace is concealed above a ceiling or installed in an attic, there should be an area provided in front of the furnace for maintenance personnel to access the unit.

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Natural Gas Regulators

Gas supplied to the building is usually more than the furnace can handle. At the gas meter there should be a gas regulator that reduces the gas pressure from the utility before it enters the meter. The utility company usually sets the downstream pressure between 5 and 7” W.C. (1.2 to 1.7 kPa), or what is required for special equipment. For a gas furnace that is running the pressure can vary by make and model but should be in the 3.5” W.C. (0.87 kPa) range. There are commercial versions that have higher running pressures, be sure to check the name plate for the correct pressure. Also note the maximum pressure rating of the furnace as this value should never be exceeded. For other gas types check the manufactures literature for operating pressures.

Combustion Intake and Exhaust

A sealed combustion furnace is the best option when selecting a furnace. This is when outside air is brought directly to the combustion chamber and exhausted through the flue to the outside. This lessens the chance of combustion byproducts from entering the occupied space. With non-sealed combustion chambers, air is drawn into the unit for combustion and then exhausted through the flue. These high efficiency sealed combustion chamber units exhaust gas that is acidic and can damage old unlined chimneys. In these cases, a new flue may need to be installed or the old chimney needs to be lined.

Combustion air is required for all fuel burning appliances. If the furnace is in an enclosed space, then the proper amount of air will need to be brought into the enclosure to allow for proper combustion. No matter what the enclosure size is, there needs to be provisions for combustion air. Combustion air mixes with the fuel to provide the proper ratio for clean burning of the gas

Gas Venting

Vents are classified into one of four categories. Category I and II vents are for natural draft gas appliances that operate at a negative pressure. They depend on the natural draft of warm air. Most contractors are familiar with Type “B” double wall vent allowed under category I systems. Type “B” flue vent has an inter duct made of aluminum to resist corrosion, with an outer duct made of galvanized steel for strength with an air gap in between. Because high air rises the use of any horizontal flue pipe needs to be slopped at least a 1/4” per foot.

Category III and IV vents are operated at a positive pressure and use a fan to move flue gases out of the system. They require a tighter seal due to the positive pressure.

For condensing furnaces either direct venting or non-direct venting is used with 2” to 4” PVC piping or equivalent as approved by local codes.

Carbon Monoxide Detectors

With gas furnaces there is always the chance that the heat exchanger will leak and bypass air into the occupied space. This combustion gas is poisonous and could cause headaches, dizziness, weakness, upset stomach, vomiting, chest pain, confusion and even death. 

Install Carbon Monoxide Detectors to keep occupants Safe from Carbon Monoxide Poisoning
Install Carbon Monoxide Detectors to keep occupants Safe from Carbon Monoxide Poisoning

Remember that carbon monoxide is odorless, so you won’t smell a leak. Therefore, installing a Carbon Monoxide Sensor is so important. Also, carbon monoxide can’t be seen as it’s colorless. It also can’t be heard, so your own human senses can’t be relied upon as your eyes, nose and ears won’t detect anything before the effects of the carbon monoxide could be too late, so get CO sensors installed to protect the occupants.

Gas Ignition System

Whenever there is a demand for heating, the furnace needs to ignite the gas in a safe manner. Large systems will use a two-step process, where the first step is to ignite a pilot flame and once confirmed will initiate the main burners. 

Old furnaces used a standing pilot where a small amount of gas was always burning in wait for a call for heating. Current gas ignition designs use some form of automatic ignition device without the need for a standing pilot flame.

Furnace Safety Switches

Safety is paramount when supplying a combustible fuel to an appliance that serves occupied spaces. There are various safety devices contained within the furnace to provide for safe operation, in addition to installation requirements for safety. 

Flame sensors ensure that the gas has ignited and that there is a flame burning. If the flame didn’t light for some reason and the gas valve had opened, the space could fill with gas and cause a possible explosion. 

A Rollout switch senses if the burner flame is rolling backwards out of the heat exchanger. The rollout switch senses the flame and shuts off the flow of gas to prevent a fire.

Furnace Safety Switches
Furnace Safety Switches

A High Temperature Limit Switch prevents excess temperatures from occurring. Excess temperatures are an indication that something might have failed or malfunctioned. The High Limit switch will shutoff the gas if the discharge air temperature exceeds the limit. The high limit switch will have to be manually or automatically reset. If automatic, then the gas valve will be reopened when the temperature drops below the limit.

Operation and maintenance clearance requirements. Check the furnace manufacturers literature for the clearance requirements around the furnace. These clearances are for safety reason, such as preventing a fire from occurring to the surrounding construction materials. Clearances are also established for proper access to internal components for maintenance personnel. 

Furnace Rating AFUE Rating

The annual fuel utilization efficiency (AFUE) indicates a furnaces efficiency. The higher the value the greater the efficiency. You can find the efficiency listed on the front of the furnace as its required by the Federal Trade Commission to be posted. The efficiency is given as a percentage, indicating how efficient the furnace is in converting the energy from fuel into useful heat on an annual basis.

Furnace AFUE Rating
Furnace AFUE Rating

The annual fuel utilization efficiency (AFUE) is a ratio indicating the total annual heat provided divided by the total fuel consumed. A ratio of 90% would indicate that 90% of the fuel was efficiently converted into heat, while 10% was wasted. This ratio is for the furnace only and not the distribution of the heat to the space through ductwork, as poorly insulated ducts will reduce the efficiency of the overall system. 

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Maintenance of your Furnace

Be sure to change your filters often as clogged filters can cause airflow restrictions. With less air flowing over the heat exchanger, it could cause the heat exchanger to become too hot leading to cracking. The cracked heat exchanger would then leak carbon monoxide into the occupied space endangering the lives of the occupants.

Make sure to have your furnace inspected every year including a full-system cleaning, removing all dirt, soot, or corrosion. The inspection will help identify any potential problems with the furnace. Its important that the heat exchanger be inspected for any possible cracking or problems.

Install CO sensors close to all rooms used for sleeping. These can be battery operated or battery backed up versions. 

Make sure to regularly check that the CO monitors are operating properly.

Inspect the condition of the flue vent and all connections to ensure a properly sealed system.

Clean and lubricate the fan blower.

Retrofitting Existing Furnaces

A retrofit of an existing furnace can increase it energy efficiency. The additional cost to make the retrofit needs to be evaluated against a new replacement unit. If you plan on adding air conditioning, then a new system is warranted. Remember you’re not only saving on your fuel bill but you’re reducing carbon dioxide emissions. 

Before you upgrade your furnace, it’s recommended that you evaluate the potential to reduce the size of the furnace by upgrading to energy efficient windows or adding insulation to the building.

How Furnaces Work

How do Air Conditioners Work

MEP Academy Instructor
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How do Air Conditioners Work

How do Air Conditioners Work? The purpose of your air conditioner is to remove heat from inside your home or building and reject it to the outside, in addition to removing moisture and filtering the air. We’ll learn how an Air Conditioner does this by moving heat around using a refrigerant. We’ll also show the major components that get installed and how they’re connected together.

If you prefer to watch the video of this presentation, then scroll to the bottom or click this link. How do Air Conditioners Work

How do Air Conditioners Work
How do Air Conditioners Work

First you would install the condenser or outside section where the compressor and condenser coil are located. Next install the air handler in the attic. We show this one has a horizontal air handler with a furnace. We’ll show you a vertical unit shortly. Then the indoor and outdoor sections are connected with ACR type copper tubing. Inside the copper tubing is where the refrigerant circulates between the indoor and outdoor coils. Then we need to provide a circuit breaker that can handle 208/230 volts, single phase power, and run electrical conduit and wire from the panel to a disconnect switch and then make a connection to the outdoor unit. Then will install another circuit breaker in the electrical panel for 115 volts and fed the indoor air handler.

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Next for gas/electric units using a furnace we’ll install gas piping from the gas meter to the indoor air handler. Next, we’ll need to run a condensate drain from the indoor air handler’s DX cooling coil to a drain or the tailpipe of a sink.

Next, we’ll connect the return air ductwork to the indoor air handler and provide a filter grill in the ceiling for easy access for filter changeouts. Next we need to install the supply ductwork from the air handler to each room that will get supply air. These are the basics of how a split system air conditioner is connected.

And, here is what it might look like if you’re using a vertical unit. There is a move to go all electric and get away from burning fossil fuels, so the use of Heat Pumps seems to be increasing. If installing a heat pump there is no need for gas piping or a furnace as the Indoor and outdoor coils change to accommodate the requirement for either heating or cooling. See our video on “How Heat Pumps Work” for a better description.

How Heat Moves

If you left a hot cup of coffee on the table, it would lose its heat to the surrounding air and eventually its temperature would be close to the indoor air that surrounds the cup. This is how heat transfer works, heat always tries to equalize itself with the cooler surroundings, so any heat in the air will be attracted to the cold surface of the coil.

The 2nd Law of Thermodynamics - Heat always moves from a warmer object to a cooler one
The 2nd Law of Thermodynamics – Heat always moves from a warmer object to a cooler one

The second law of thermodynamics states that “Heat always moves from a warmer object to a cooler one, and seeks equilibrium”. One more example is if you had a glass filled with ice water sitting outside during a hot summer day, the heat from the air would transfer into the ice water causing the ice to melt and the water to reach the outdoor air temperature.

Refrigerant

A special substance called a refrigerant circulates through the piping of the air conditioner from the indoor coil to the outdoor coil. The refrigerant is designed to absorb heat from indoors and reject the heat outdoors. The refrigerant does this by changing from a liquid to a gas and then back to a liquid.

Refrigerant - Adding Refrigerant to a Split-System Air Conditioner
Refrigerant – Adding Refrigerant to a Split-System Air Conditioner

Refrigerants absorb heat when it changes from a liquid to a gas, and then gives up its heat when changing back from a gas to a liquid. The refrigerant is pumped around from the indoors to the outdoors by a compressor, while constantly changing from a gas to a liquid and then back to a gas again, repeatedly. For a better explanation of the refrigerant cycle see our video “Refrigeration Cycle 101”.

Compressor

The compressor is like a pump which uses electricity to power a motor, which causes the refrigerant to move around the piping circuit while increasing the temperature and pressure of the refrigerant before sending it to the condenser coil. There must be a difference in pressure between the high-side and the low-side for the refrigerant to move and for oil to return to the compressor. The compressor causes this difference in pressure and makes the refrigerant circulate through the system. The low-side being the indoor evaporator, and the high-side being the outdoor condenser coil. In a heat pump system these heat exchangers can be reversed and serve the opposite purpose.

Refrigerant Circuit
Refrigerant Circuit

The compressor raises the temperature and pressure of the refrigerant so that the heat in the refrigerant is above the outdoor design temperature. Remember that heat transfers from the warmer item to the cooler one. So, if the outdoor temperature is 95°F (35°C), then the refrigerant in the condenser needs to be above that to transfer the heat out of the refrigerant to the warm outdoor air. As the temperature of the air outdoors approaches the temperature of the refrigerant in the condenser, the heat transfer capabilities are diminished. Therefore, air conditioners struggle on super-hot days. 

The condensing temperature of refrigerant R410A can be around 115°F to 120°F (46°C to 49°C) at a pressure of 391 to 418 psig, so if the outdoor temperature gets close to this the capacity of the air conditioner will decrease.

Evaporator Coil and Supply Fan

The heat is absorbed by having a supply fan blow warm air over a cold coil located indoors, which is called the evaporator. The liquid refrigerant circulating inside the cooling coils low-pressure evaporator will turn into a gas as it absorbs the heat from the warm air passing over it, like water that boils in a pot on the stove when heat is added. Since the refrigerant is much colder, 42°F to 45°F (6°C to 7°C), this causes the heat to transfer from the warm air to the colder refrigerant in the coil, causing the air to become cooler.

Air Handler Blower Fan and "A" Coil
Air Handler Blower Fan and “A” Coil

The evaporator will also remove moisture from the air in addition to cooling the air. The change in temperature is considered sensible cooling, while the removal of moisture is considered latent cooling. Like that glass of ice water sitting outside, the air surrounding the glass meets the cold glass surface and the moisture in the air condenses out onto the glass. A similar event occurs on the cooling coil, as the warm air drops in temperature when it meets the cold coil some of the moisture or water vapor will condense on the cooling coil and become condensate. The condensate will drip off the coil into a drain pan where it is connected by a pipe leading to the sewer, drywell, or the tailpiece of a sink.

Condenser Heat Exchanger and Fan

The condenser heat exchanger is located outside, where the refrigerant will reject the heat to the outdoor air. The outdoor condenser section is where the compressor, heat exchanger and condenser fan are located, this is considered the high-side of the system. 

Condenser - Outdoor Section with Compressor, Condenser Coil and Fan
Condenser – Outdoor Section with Compressor, Condenser Coil and Fan

This is called an air-cooled condenser because the fan blows air over the coil that facilitates the heat transfer , as opposed to a water-cooled condenser. Remember that heat moves from the warmer to the cooler medium. Even though the outdoor air is warm, the refrigerant is warmer, allowing heat to transfer from the condenser to the outdoor air. Remember the compressor raised the pressure and temperature of the refrigerant.

Upflow Furnace with "A" Coil (Vertical Furnace)
Upflow Furnace with “A” Coil (Vertical Furnace)

The problem comes about when it is exceptionally hot outside, then the temperature of the outdoor air and the refrigerant are getting closer to each other and the transfer of heat is slowed down, causing a loss of cooling capacity. Most condenser are rated for an outside design temperature of 95F. When the temperature outdoors exceeds this amount the system becomes derated, meaning that less cooling capacity is available. The refrigerant leaving the condenser passes through the expansion valve.

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Expansion Valve

The expansion valve controls the volume of refrigerant that passes from the outdoor condenser coil to the indoor evaporator coil.

Expansion Valve by Parker - Sporlan
Expansion Valve by Parker – Sporlan

The compressor increased the pressure of the refrigerant and now the expansion valve lowers the pressure as the refrigerant is metered through the valve from the high-side to the low-side. This is how the cooling capacity is controlled, the more refrigerant that is let through, the more heat that can be absorbed from the space. 

Thermostat

The thermostat is the main controller that you use to call for cooling or heating, and where you set your requirements for space temperature. 

Cooling Capacity

The air conditioners cooling capacity is rated in tons. Tons is not an indication of its weight, but of the air conditioners cooling capacity. One ton is equal to 12,000 Btuh, which is an expression of the ability of the air conditioner to remove heat. The higher the number, the more heat that can be removed from a building. 

When shopping or being quoted an air conditioner, the contractor may quote the tonnage of the unit to be installed, or the btu’s per hour. Either way you can determine the value of the other as (1-Ton = 12,000 BTUH). The thermostat maybe set low to provide more cooling, but the system will be at maximum capacity if it’s on an exceptionally hot day. The capacity of the air conditioner is determined by doing a load calculation. For additional information see our video “What is a Ton of Air Conditioning”.

Load Calculation

Contractors and engineers have available to them the ability to size air conditioners using Load Calculation software. To get an accurate determination of the cooling load, which is required to size the air conditioner correctly, load calculation software should be used. The load calculation program will take into consideration the buildings orientation to the sun for a proper solar load. The determination of the composition of the walls, glass, doors, and roof are important as their “R” values determine the rate at which heat is transferred through them. The square footage of the home or building will also be considered. All of this is easily done with a load calculation program.

Air conditioners should never be sized using rule of thumb values, as there is a tendency to oversize the unit which causes more problems. A few of the problems of oversizing is the additional initial cost of the equipment and installation, and the possible poor performance of moisture removal. When air conditioners are oversized the air conditioner cools faster than normal, which causes it to frequently turn on and off. When an air conditioner cycles on and off frequently it doesn’t allow enough time for moisture removal. This could mean a cool, but damp space. Oversizing also leads to increased energy bills, additional maintenance cost and early equipment replacement cost due to an increase in the on and off cycling times. Oversized air conditioners won’t run efficiently, and energy efficiency is critical for a cost effective system.

Energy Efficiency of Air Conditioners

Air conditioners are given a grade for how efficient they convert electrical energy into useful cooling capacity. This is like a grade you might get in school, the better the grade, the smarter you are deemed to be about the subject. Air conditioners are rated by their Seasonal Energy Efficiency Ratio (SEER) value. The higher the number the better the air conditioner is at using the electrical energy consumed. 

SEER and EER Efficiencies of Air Conditioning Equipment
SEER and EER Efficiency Ratios

If you live in a hot and dry climate where the peak load is critical, then you will want to look at the Energy Efficiency Ratio (EER) of the air conditioner. The EER rates the unit based on the peak load conditions, which is more likely to occur in hot climates. 

How do Air Conditioners Work
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