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Domestic Hot Water Recirculation System

MEP Academy Instructor
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Domestic Hot Water Recirculation System

Domestic Hot Water Recirculation System. A lot of water gets wasted waiting for the hot water to arrive at a sink, bathtub, shower or other plumbing fixture. We’ll show you how residential and commercial domestic hot water recirculation systems work to save water, energy, time and money.

If you prefer to watch the video version of this presentation, then scroll to the bottom or click on this link. Domestic Hot Water Recirculation System

We’ll start by showing you three basic residential systems. Domestic hot water recirculation systems are designed to provide instant hot water to various fixtures and appliances throughout a home, such as faucets, showers, and washing machines, by circulating hot water continuously through the pipes, so as to avoid waiting for the water to heat up.

System #1 is the Traditional Residential System with a Dedicated Return Line.

Hot water recirculating system
Hot water recirculating system
  1. A dedicated return line is installed that connects the furthest hot water fixture in the home back to the water heater. This line allows hot water to circulate continuously back to the water heater in a continuous loop.
  2. A recirculation pump is installed on the hot water return line, typically near the water heater. The pump is designed to move hot water from the farthest fixture through the dedicated return line back to the water heater.
  3. A check valve is installed on the return line to prevent hot water from flowing back into the return piping.
  4. A timer or thermostat is installed to control when the recirculation pump operates. To ensure that the recirculation system operates efficiently, a temperature sensor or timer is installed near the pump. The sensor or timer controls the pump to circulate hot water only when needed.
  5. When hot water is needed at a fixture, the pump is activated and hot water is quickly circulated through the pipes, providing hot water almost instantaneously.
  6. The return line ensures that hot water is constantly recirculated, so there is always hot water available when needed.

If the home wasn’t pre-piped with a dedicated return line, then the following two options are available to avoid an evasive renovation project.

Under the Sink Residential System #2

A bypass valve is installed at the furthest fixture to allow the hot water line to circulate back to the water heater using the cold water piping. The Bypass valve stays closed while the hot water temperature is warm.

Hot water recirculation Bypass Valve under furthest fixture
Hot water recirculation Bypass Valve under furthest fixture

A pump is installed on the hot water line at the water heater. When the temperature of the water at the furthest plumbing fixture cools down the pump will turn on and circulate hot water from the water heater through the bypass valve and into the cold water line until the temperature is warm enough. The pump is turned on by a timer that is set by the user to come on when the residents normally need hot water.  The system can be easily installed within a couple of hours.

Under the Sink Residential System #3

Domestic Hot water recirculating pump under sink
Domestic Hot water recirculating pump under sink

There is a simple on demand hot water recirculation system that can be added to the furthest fixture, in our case a pump is added to the sink on the second floor of this home. The piping is reconfigured so that the water is fed through the recirculation pump housing manifold. The manifold is then connected to the sink. There is no hot water recirculation line, instead the pump has a temperature sensor that will shut off the pump when the temperature reaches it setpoint of 110F (43C), or whatever the customer sets it at. A little of the hot water will be sent into the cold water line until the temperature sensor shuts off the pump.

There are options on how to control the pump. By installing an Aquastat or temperature sensor the pump can turn on when the hot water temperature drops to 85F (29C) and keep running until the stat reads 105 F (40 C), at which point it shuts off. 

Another option is that there could be a timer set to bring the pump on at a certain time each day, lets say 6:00 am, a half hour before the family gets up. This would allow for the hot water to be ready for use at any fixture. 

Another option is a switch that is manually turned on or remotely if using a wireless App. With this option the pump could be set to turn off and on every 15 minutes to maintain hot water at the fixtures.

This avoids wasting time waiting for hot water, saves money and stops wasting water.

Commercial Hot Water Recirculation System

When selecting a commercial hot water recirculation system, it is essential to consider factors such as the building’s size, water usage patterns, and energy efficiency goals. 

Domestic hot water recirculation system in a commercial application
Domestic hot water recirculation system in a commercial application

Here is a simple explanation using a small hotel with one main riser.

A hot water recirculation pump will be installed along with a dedicated return line that is connected to the hot water piping at a point that provides a maximum of 50 feet in piping distance to the furthest fixture requiring hot water. The International Plumbing Code IPC, section 607.2 states that the distance from the source of hot water to the fixture shall not exceed 50 feet.

Then a check valve along with the discharge piping is connected to the cold water piping feeding the water heater. This is the basic layout. Of course there are many factors to consider when designing a commercial system so consulting with a qualified mechanical engineer can help ensure that the system selected is appropriate for the building’s specific needs and requirements.

When hot water is turned on at a fixture or appliance, the water in the dedicated return line is pushed back to the water heater. The pump then circulates hot water from the water heater through the dedicated return line, and the hot water is quickly available at the fixture or appliance.

Overall, a domestic hot water recirculation system can save water and energy by reducing the amount of time it takes for hot water to reach fixtures and appliances, and by minimizing the amount of water that is wasted while waiting for hot water to arrive.

Some recirculation systems use a thermostatic valve at each fixture, which automatically turns on the pump when the water temperature drops below a certain level. This can save energy by reducing the amount of time the pump needs to run.

Overall, a domestic hot water recirculation system can provide convenience and save water by reducing the amount of time it takes to get hot water at a faucet or shower.

Various Recirculation System Types

There are various types of commercial hot water recirculation systems available in the market, including:

  1. Pump-based systems: In this type of system, a pump is installed in the hot water line, which circulates hot water continuously through the pipe. A return line is also installed, which sends the cold water back to the water heater.
  2. Demand recirculating systems: In this type of system, a pump is activated only when there is demand for hot water at a specific faucet or fixture. This system typically uses a thermostatic valve to regulate the water temperature and a timer to control the pump.
  3. Gravity-fed recirculating systems: This system uses the natural convection of hot water to circulate it throughout the building. The system is designed so that the hot water rises to the upper floors of the building and then circulates back down through the return line.

Commercial hot water recirculation systems can save significant amounts of water and energy by reducing the time it takes for hot water to reach the tap. They are commonly used in hotels, hospitals, schools, and other commercial buildings where hot water demand is high.

Benefits of Hot Water Recirculation Systems

There are several benefits to using a hot water recirculation system in a commercial or residential building, including:

  1. Improved energy efficiency: With a hot water recirculation system, hot water is constantly flowing through the pipes, reducing the amount of time it takes for hot water to reach its destination. This can result in significant energy savings, as less energy is required to heat the water.
  2. Increased convenience: With a recirculation system in place, hot water is always available when needed, which can be a significant convenience for businesses that rely on hot water for their operations.
  3. Reduced water waste: By reducing the amount of time it takes for hot water to reach its destination, a recirculation system can also reduce water waste, as less water is wasted while waiting for hot water to arrive.
  4. Improved hygiene: With hot water readily available at any tap or fixture, businesses can ensure that their employees and customers have access to hot water for hand washing and other hygiene-related activities.

Domestic hot water recirculation systems work by continuously circulating hot water from the water heater through a dedicated loop of pipes to the fixtures that require hot water, such as faucets and showers. This helps to reduce the amount of time it takes for hot water to reach these fixtures, which can help conserve water and energy.

Overall, hot water recirculation systems can provide a convenient and efficient way to deliver hot water to fixtures, while also reducing water waste and improving energy efficiency.

There are several types of hot water recirculation systems available for commercial use, including traditional and demand-controlled systems. Traditional systems continuously circulate hot water through the pipes, while demand-controlled systems only operate when hot water is needed. The choice of system will depend on the specific needs and requirements of the business in question.

ASHRAE 90.1-2022

7.4.4.2 Temperature Maintenance Controls

Systems designed to maintain usage temperatures in hot-water pipes, such as recirculating hot-water systems or heat trace, shall be equipped with automatic time switches or other controls that can be set to switch off the usage temperature maintenance system during extended periods when hot water is not required.

7.4.4.3 Outlet Temperature Controls

Temperature controlling means shall be provided to limit the maximum temperature of water delivered from lavatory faucets in public facility restrooms to 110°F.

7.4.4.4 Circulating Pump Controls

When used to maintain storage tank water temperature, recirculating pumps shall be equipped with controls limiting operation to a period from the start of the heating cycle to a maximum of five minutes after the end of the heating cycle.

Timer Control

The pump is turned on and off according to a programmed schedule.

If schedule is set to have the pump off when hot water is requested, then water will be wasted.

Temperature Control

With the use of a temperature-controlled system, the pump will turn on and off to maintain the temperature setpoint on the return water piping, usually 120F.

This method keeps a minimum return temperature.

Temperature Modulation Control

This is a mixture of temperature control and scheduled control. The temperature of the domestic hot water supply is changed throughout the day based on the occupancy usage patterns. This could be high demand in the early morning for multifamily residential buildings where occupants are waking up and preparing for their daily activities or going to work. This method attempts to match occupancy behavior to a schedule for setting hot water supply temperatures.

Demand Control

Hot water demand for this method of control uses real-time user input and return water temperature. The pump will run if the controls detect water flow, and the temperature of the return water has dropped to a certain minimum setpoint such as 100F.

Demand control and temperature modulation work the best when combined into one system approach for energy and water savings

Summary

Hot water recirculation systems are typically installed to improve energy efficiency, reduce water waste, and enhance user convenience. By circulating hot water through the building’s supply lines, these systems can minimize the amount of water that goes to waste while waiting for hot water to arrive at the faucet or showerhead.

When designing a domestic hot water system use a compact layout where the distribution to any fixture requiring hot water is a short distance from the source. Install a recirculation pipe with short branches to each fixture requiring hot water.

Domestic Hot Water Recirculation System

How Heat Recovery Wheels Work

MEP Academy Instructor
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How Heat Recovery Wheels Work

How Heat Recovery Wheels Work. Heat recovery wheels, also known as heat wheels or rotary heat exchangers, are a type of energy recovery device that are commonly used in HVAC (Heating, Ventilation, and Air Conditioning) systems to recover and reuse the heat energy that would otherwise be lost to the environment. Heat recovery wheels are designed to work by transferring heat between two air streams that are flowing in opposite directions, without mixing the two air streams together. We’ll show you how they’re used in a hospital and a locker room at your local gym.

If you prefer to watch the video of this presentation, then scroll to the bottom or click oaths link. How Heat Recovery Wheels Work.

Heat Recovery Wheel serving a Hospital operating Room
Heat Recovery Wheel serving a Hospital operating Room

Here’s how Heat Recovery Wheels work.

  1. Heat recovery wheels are typically installed in the supply and exhaust air ducts of an HVAC system. The supply air duct carries fresh air into the building, while the exhaust air duct carries stale air out of the building.
  2. As the two air streams flow past each other, the heat recovery wheel rotates to transfer heat energy from the warm, stale air to the cool, fresh air. This transfer of heat energy occurs using a heat-absorbing material that is typically made of aluminum or a similar metal for sensible wheels and a moisture absorbing material like silica gel or a zeolite molecular sieve for an Enthalpy recovery Wheel.
  3. The heat recovery wheel works by capturing the heat energy from the outgoing air stream as it passes through the heat-absorbing material. The wheel then rotates and transfers this heat energy to the incoming air stream as it passes through the same material in the opposite direction.
  4. As a result, the fresh air entering the building is pre-heated, while the exhaust air leaving the building is cooled. This helps to reduce the overall energy consumption of the HVAC system, as less energy is required to heat or cool the incoming air.
  5. Heat recovery wheels are most effective in climates where there is a large temperature difference between the indoor and outdoor air. In colder climates, the wheels can help to reduce heating costs by pre-heating the fresh air, while in warmer climates, they can help to reduce cooling costs by pre-cooling the fresh air.
  6. Energy recovery wheels can be a separate piece of equipment or come pre-installed in an air handler.

It is important to note that proper maintenance and cleaning of the heat recovery wheel is essential for optimal performance and energy savings. Dirty or clogged wheels can reduce the effectiveness of the system and lead to increased energy consumption.

Checkout these Heat Recovery Systems here

There are several types of Heat Recovery Wheels. One type will capture sensible heat only and the other is an enthalpy wheel, often referred to as a desiccant wheel, which will capture sensible and latent heat.

Heat Recovery Wheel in Air Handler serving a locker room
Heat Recovery Wheel in Air Handler serving a locker room

Sensible Heat Wheel

With the use of a sensible heat recovery wheel the dry bulb temperature of the air will be increased or decreased depending on the outdoor temperature and setpoint. There will be no effect upon the moisture content or latent heat of the air, as no moisture is transferred between the two air streams.

Energy Recovery Wheel
Energy Recovery Wheel

Enthalpy Wheel

With the use of an enthalpy wheel or total energy wheel, the moisture content or latent heat of the air will be affected. Both sensible and latent heat will be transferred using an enthalpy wheel. The amount of moisture transferred is dependent on the amount of water vapor in the air. Moisture is transferred between the two airstreams using a desiccant which absorbs or adsorbs water vapor from the high-pressure vapor airstream and releases it into the lower pressure vapor airstream.

Capacity Control of Heat Recovery Wheels

When the load of the system varies the wheel can adjust its speed using a variable frequency drive (VFD), or a bypass duct can be installed around the wheel to reduce the volume of air that travels through the heat recovery wheel.

Heat Recovery Wheel Effectiveness

The effectiveness of the heat recovery wheel is determined by how much of the energy is transferred between the two airstreams. This is affected by the amount of air flow and the difference in energy between the two airstreams. The calculation looks like this.

Equation for Effectiveness. E = [Vs x (T1 – T2)] / [Vmin x (T1 – T3)]

E       = Effectiveness

T1      = Outside Air Temperature (°F DB) or Enthalpy (btu/Lb.)

T2      = Supply Air Temperature (°F DB) or Enthalpy (btu/Lb.)

T3      = Return Air Temperature (°F DB) or Enthalpy (btu/Lb.)

Vs      = Volume of Supply or Outside Air (CFM)

Vmin   = Volume Minimum. Lowest CFM, either Supply or Outside Air (CFM)

Using the standard equation for heat transfer, we can modify it to include our effectiveness factor to determine the total heat transferred by the heat recovery wheel.

Sensible Heat Transfer Equation

Standard Equation. Qs = CFM x 1.08 x Delta-T (T1 – T3)

Modified Equation. Qs = E x CFM x 1.08 x Delta-T (T1 – T3)

Total Heat Transfer Equation

Standard Equation. QT = CFM x 4.5 x Delta-Enthalpy (h1 – h3)

Modified Equation. QT = E x CFM x 4.5 x Delta-Enthalpy (h1 – h3)

E       = Effectiveness (Sensible or Total)

Qs     = Sensible Heat Transferred (btu/hr.)

QT     = Total Heat Transferred (btu/hr.)

h1      = Outside Air Enthalpy (btu/Lb.)

h3      = Return Air Enthalpy (btu/Lb.)

The Heating Season for Heat Recovery

When heating is required and the temperatures outside are very cold, the use of a heat or energy recovery wheel can save energy by removing heat from the exhausted airstream. No matter what the season an energy recovery wheel can retrieve needed heat or expel unwanted heat from the airstreams.

ASHRAE 62.1 Air Classifications

Air is classified according to ASHRAE 62.1. The classification indicates whether the air can be recirculated within the same space or transferred to another space based on the classification of that space.

In the above image we show an air handler providing 100% outside air to a locker room and gym. The air handler has a heat recovery wheel to capture energy that would otherwise be wasted. The locker room in our example is considered Class 2 air and can be recirculated within the same space or other Class 2 spaces which includes the GYM portion of the building. Air is classified according to ASHRAE 62.1. The classification indicates whether the air can be recirculated within the same space or transferred to another space based on the classification of that space.

Another method is to remove the fan coils and just feed the space with the Air Handler which has a chilled water and heating hot water coil.

Checkout these Heat Recovery Systems here
How Heat Recovery Wheels Work

Refrigerant Piping Design Basics

MEP Academy Instructor
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Refrigerant Piping Design Basics

Refrigerant Piping Design Basics. Refrigerant piping design is an important aspect of any air conditioning or refrigeration system. Proper design of the refrigerant piping system ensures that the system operates efficiently and reliably. Here are eight key factors to consider when designing refrigerant piping.

If you prefer to watch the video of this presentation, then scroll to the bottom or click the following link. Refrigerant Piping Design Basics

1. Refrigerant System Layout

The layout of the refrigerant system should be designed to minimize the length of the piping and the number of fittings and inline components required. This reduces pressure drop in the system and helps improve efficiency. The total length of the refrigerant piping must not exceed the manufacturers requirements as this could result in a loss of capacity.

2. Refrigerant Pipe Sizing

The diameter of the piping should be chosen based on the required refrigerant flow rate and pressure drop. The wrong size piping can cause excessive pressure drops, leading to reduced system efficiency and capacity, while increasing power consumption. 

Liquid lines that are installed larger than required will increase the amount of refrigerant in the system, which could create additional problems. While under sizing liquid lines can cause the refrigerant to flash before it reaches the expansion valve, which will starve the evaporator and cause a loss in capacity, and the possible frosting up of the coil.

If the suction line is oversized then there could be problems with the return of oil to the compressor. And, if they are undersized there can be a loss of capacity and an increase in superheat.

3. Refrigerant Type

Different refrigerants have different properties, such as pressure, temperature, and viscosity. The refrigerant type should be considered when designing the piping system, and the system should be designed to accommodate the specific characteristics of the refrigerant used.

4. Refrigerant Piping Materials

The materials used for the piping should be compatible with the refrigerant and should be able to withstand the pressure and temperature of the system. ACR type Copper tubing is commonly used for refrigerant piping in the HVCAR industry.

Checkout Refrigerant Piping Products here

5. Refrigerant Piping Insulation

Proper insulation is necessary to prevent refrigerant lines from losing their cooling capacity. The thickness of the insulation should be chosen based on the temperature difference between the refrigerant and the surrounding environment. Insulation thickness requirements can be found in the various codes that regulate the installation of the refrigerant piping. See our video on the proper methods for insulating refrigerant piping.

Checkout Refrigerant Insulation Products here

6. Refrigerant Piping Support

Refrigerant piping should be supported at regular intervals to prevent sagging and vibration, which can cause leaks and reduce system efficiency.

7. Expansion and Contraction

The refrigerant piping should be designed to accommodate the expansion and contraction of the piping due to temperature changes. Long lengths of piping can cause problems when temperature changes with the piping vary. The piping length will grow when heated up and contract when cooled down. Some method of compensating for the variable of expansion and contraction must be considered. 

Copper Piping Expansion = Delta-Temperature in piping x Piping Length x Coefficient of Expansion

8. Refrigerant Oil Management

Oil will be circulated around the system with the refrigerant and must be returned to the compressor where it’s needed to provide lubrication of bearings and moving parts. For this to happen it’s important that the refrigerant piping is sized correctly including the refrigerant velocity.

As refrigerant changes from a liquid to a vapor in the evaporator, the oil is separated out, which requires the correct velocity to ensure that the oil returns to the compressor. It’s important that refrigerant oil return to the compressor at the same rate at which it leaves.

Refrigerant Carrying Capacity of Piping

Refrigerant pipe sizing will also dictate the quantity of refrigerant required, as the larger the liquid line pipe size, the greater the volume of refrigerant required. We’ll look at the liquid line because it holds more refrigerant per linear foot than that of the same size suction line. We’ll compare the difference between 100 feet of pipe for various sizes using standard pressure in a R22 and R410A system.

R22 (100 feet of Liquid Line)

1/2” Pipe = 7 Lbs.

5/8” Pipe = 11.3 Lbs.

Difference in 4.3 Lbs.

So, by upsizing your liquid line from a 1/2” to a 5/8” line, the system would require approximately 4.3 Lbs. more of R22 refrigerant.

R410A (100 feet of Liquid Line)

1/2” Pipe = 5.8 Lbs.

5/8” Pipe = 9.2 Lbs.

Difference in 3.4 Lbs.

So, by upsizing your liquid line from a 1/2” to a 5/8” line, the system would require approximately 3.4 Lbs. more of R410A refrigerant.

When to Use Soft Copper

This is bound to create some controversy, as the ease by which soft copper can be installed is compelling from a labor standpoint, but practical engineering guidelines should be considered. Keeping soft copper installation to a maximum of a 50-foot roll is a prudent engineering request. Long lengths of soft copper tend to sag, and oil could be trapped where sags occur in the suction line.

Purging

When brazing refrigerant piping it’s important that a constant nitrogen purge be used to keep the system clean from the formation of copper oxides.

Refrigerant Pressure Drop Guidelines

The compressor will need to work harder for added pressure drop in the refrigerant piping design which considers pipe size, equivalent piping length which includes inline fittings, and components. Components may need to be oversized to compensate for excessive pressure drop in the system. By installing piping that’s too small there will be an increase in pressure drop and velocity, and a reduction in system capacity. It’s important that the overall equivalent pipe length be considered when selecting refrigerant pipe sizes.

Total pressure drop in the refrigerant piping system is determined by many factors including the pressure, velocity, and friction through pipe, valves, and fittings. And as previously stated, there is a loss in capacity of the system if the suction line is undersized. Smaller pipes have greater pressure losses, so ensuring the correct size is important for meeting design capacity.

Refrigerant Volume

It’s important to have the correct mass of refrigerant to achieve the design capacity of the system.

Sizing Refrigerant Piping

The process of sizing refrigerant piping begins with measuring the distance between the outdoor condensing unit and indoor fan coil while counting all the inline fittings and components. The routing should minimize the length of piping and number of fittings required, as each fitting or valve increases the overall pressure drop of the system. Upsizing the liquid line one size will increase the refrigerant carrying capacity by about 50% more, for example a 1/2” liquid line carries approximately 5.8 lbs. of R410A per 100 feet, while a 5/8” liquid line carries about 9.2 Lbs./100 feet.

If the pressure drop is too great in the liquid line, then it’s possible that the pressure drops below the saturation temperature of the refrigerant causing it to flash into vapor. This cause a loss in capacity and explains why the correct sizing of the piping is important, and why you should avoid additional fittings or too small of a liquid line. 

When the condenser is below the air handler than the Liquid Line requires “Vertical Lift”, and when the condenser is above the air handler than the suction line requires “Vertical Lift”. This is easy to determine if you think about the work the compressor must do, and where the compressor is located when running. If it’s on the bottom then it must push up, and if it’s on the top then it must pull up. Depending on where the compressor is in relationship to the air handler it either must push the liquid up or pull the suction gas up.

Summary

Overall, the refrigerant piping design should be carefully considered to ensure that the system operates efficiently and reliably. A well designed system will ensure that the suction, liquid and discharge piping is large enough to prevent excessive pressure drop, yet small enough to ensure that the velocity will carry the oil back to the compressor crankcase. It’s recommended to consult with a professional HVAC engineer to ensure proper design and installation.

Refrigerant Piping Design Basics

How Indirect Evaporative Coolers Work

MEP Academy Instructor
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How Indirect Evaporative Coolers Work

We’ll learn how indirect evaporative coolers work. By using indirect evaporative cooling some buildings can eliminate mechanical refrigeration-based systems while reducing environmental impact. Indirect evaporative coolers use air to air heat exchangers to optimize approach temperatures. We’ll show you four systems that use the indirect evaporative cooling method.

If you prefer to watch the Video of this presentation than scroll to the bottom or click the following link. How Indirect Evaporative Coolers Work

The difference between a direct evaporative cooler and an indirect evaporative cooler is that a direct evaporative cooler will add moisture to the air, thereby increasing the humidity, and the indirect evaporative cooler doesn’t add moisture to the space. 

Checkout these Indirect Evaporative Coolers here

When water evaporates from a liquid to a vapor by the process of the heat of vaporization, sensible heat is absorbed from the air causing the air temperature to drop.

Indirect evaporative coolers use two separate air streams separated by the heat exchanger walls. The secondary air stream uses the evaporative process where water trickles down over air being exhausted from the building or by the use of outside air. This causes some of the water to evaporate and absorb heat from the primary air stream through the heat exchanger wall.

Primary and Secondary Air in a Evaporative Cooler Heat Exchanger
Primary and Secondary Air in a Evaporative Cooler Heat Exchanger

The heat exchanger keeps the wet air stream separate from the primary dry air flow to the space. Indirect evaporative coolers work best in low humidity areas with design wet bulb temperatures below 70F, allowing for an energy savings over mechanical refrigeration cooling.

The use of air conditioners contributes to the largest consumption of peak demand on the US electricity grid and is the primary cause of blackouts and grid failures. The problem is increased on high ambient temperature days when air conditioners are least efficient and the demand for cooling is the greatest. Indirect evaporative coolers use less energy than Variable Air Volume or Direct Expansion (DX) rooftop packaged units.

How indirect Evaporative Coolers Work

There are various configurations that can be used with indirect evaporative coolers, including additional stages of cooling using direct evaporative cooling and chilled water or DX cooling for additional capacity. We’ll explain the basic Indirect Evaporative Cooler only application.

The secondary air can be Return air from the space or outside air that enters the indirect evaporative cooler and passes over a wetted Heat Exchanger medium where the water is evaporated before its discharged outdoors. On the primary side the Outdoor air is brought into the indirect evaporative cooler where it crosses the Heat Exchanger medium without mixing with the return air and is indirectly cooled by encountering the cool heat exchanger before being supplied to the space. 

If additional cooling is required, then a second or third stage of cooling can be added with an direct evaporative section and a chilled water or DX coil to drop the supply air temperature further. Since the primary air never mixes with the secondary wet air, the humidity of the space is not increased.

Indirect Evaporative Cooling in a Data Center

An indirect evaporative cooler can be used to cool a data center while saving large amounts of energy. See our video on Data Centers for a better explanation of the systems used for cooling data centers. Hot air from the servers is captured in a Hot Aisle and brought into the indirect evaporative cooler where it travels through the primary side of the heat exchanger where it gives up its heat to the secondary side. See our video on Heat Exchangers for a better understanding of Plate and Frame Heat Exchangers. 

Indirect Evaporative Cooler in a Data Center
Indirect Evaporative Cooler in a Data Center

The cold air is then sent back to the data center through an underfloor distribution system. The cold air exits through floor grilles and travels back into the server racks where it picks up the heat of the servers and begins the cycle again. On the secondary side of the indirect evaporative coolers heat exchanger, there are fans mounted on top of the unit that pulls outside air through the heat exchanger as water is sent trickling down causing the water to evaporate and absorb heat through the walls of the heat exchanger. 

Checkout these Indirect Evaporative Coolers here

If the indirect evaporative process can’t meet the load because of unfavorable outdoor ambient conditions, a second phase of cooling can be added. This secondary cooling can be achieved by using a DX or Chilled Water coil.

Indirect Evaporative Cooling of Air-Cooled Chillers

Indirect evaporative cooling is also used to cool down the condenser coils of an air-cooled chiller.

Air-Cooled Chiller
Air-Cooled Chiller

Panels containing wetted medium can be attached around the air-cooled chiller, effectively closing off the pathway for the condenser fan inlet air. This causes the condenser inlet air to travel through the media which is sprayed with water based on the ambient temperature and the compressors liquid line temperature.

Air-Cooled Chiller with Evaporative Cooling
Air-Cooled Chiller with Evaporative Cooling

This precools the incoming air before it travels over the warm condenser coils, allowing for increased energy efficiency. Before attaching the panels the condenser coils should be cleaned to ensure the best performance.

Packaged Air Conditioners and Indirect Evaporative Cooling

This is another method of using indirect evaporative cooling to pre-cool air before it enters the condenser coil of a packaged DX unit. This also allows for increased efficiency.

Packaged Unit with Evaporative Cooling Pads
Packaged Unit with Evaporative Cooling Pads

Indirect Evaporative Cooling using a Fluid Cooler

There is another method of providing indirect evaporative cooling by providing a fluid cooler that feeds a cooling coil within an air handler. The fluid cooler provides indirect cooling by spraying water over an enclosed coil that circulates water through an air handler. The coil in the air handler absorbs heat from the space or outdoor air and circulates it to the tower where it gives up its sensible heat to the cool moist air. The water circulated in the Indirect Evaporative Cooler never mixes with the water circulated in the air handler coil.

Indirect Evaporative Cooling Using a Fluid Cooler

If this doesn’t provide enough cooling then a secondary system can be added, like an evaporative cooling section or a chilled water coil as shown here fed by an air-cooled chiller.

Benefits of Evaporative Cooling

  1. It can reduce or eliminate mechanical refrigeration or chiller usage.
  2. Overall energy savings
  3. Initial cost is less than refrigerated air conditioning
  4. Reduced maintenance cost with less skilled maintenance personnel. 
  5. Works good in dry climates
  6. Can save water when compared to a water-cooled chiller plant.
  7. The ability to increase the amount of outdoor air for improved indoor air quality. 
  8. Environmentally friendly as there are no refrigerants, CFC’s or HCFC’s.

Where are Indirect Evaporative Coolers Used

There is a wide application for the use of indirect evaporative coolers in schools, warehouses, offices, retail, industrial and some data centers.

According to a NREL study the use of a multi-stage indirect evaporative cooler there are “Three target market segments that have been identified for this technology: data center installations in ASHRAE climate zones 2B through 6B; outside air pre-conditioner retrofits for air-cooled RTUs in climate zones 2B and 3B; and new construction and facilities that do not currently have cooling systems in climate zones 4B, 5B, and 6B. In ASHRAE climate zones 1A through 7A, the increased outdoor humidity characteristic of these zones reduces cooling capacity and overall energy savings to the point that the multistage IEC will not provide a favorable return on investment.” 

Calculating the Effectiveness of Indirect Evaporative Coolers

The following calculation is often used to inform the engineer about the effectiveness of using an indirect evaporative cooler in a particular climate. Remember that these units work best in hot and dry climates. The higher the value the more efficient the indirect evaporative cooler.

EF = T (DB) – SAT / T (DB) – T (WB)

EF= Evaporative Effectiveness

T (DB) = Ambient Dry Bulb temperature

T (WB) = Ambient Wet Bulb Temperature

SAT = Supply Air Temperature

The greater the difference between the ambient dry bulb and wet bulb temperatures, the better the chances for the efficient use of an indirect evaporative cooler. 

Energy Use and Increased Temperatures

The typical air-cooled air conditioner loses efficiency the higher the outdoor temperature gets, while evaporative cooling usually gets more efficient. 

Summary

Indirect evaporative coolers use less energy than a refrigerant based system, they provide better air quality when ventilation air is increased, they avoid the use of environmentally hazardous refrigerants, and the installed cost is less, including the reduced skill level required of maintenance personnel. The main disadvantage is that they perform best in hot and dry climates only.

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