Heat Pump Basics

Heat Pump Basics

Heat pumps are a popular way of heating a pool. They are energy efficient and can be installed anywhere a 20 to 60 amp electrical circuit is available, depending on the BTU output.

The major pool equipment manufacturers all sell heat pumps—Pentair with the UltraTemp, Jandy with the VersaTemp JRT Series, and Hayward with HeatPro models. Good heat pumps are also manufactured by independent companies—Raypak, Aquacal, Gulfstream, Built Right (acquired by Fluidra), and others.

There is little difference in the manufacturers' heat pump technology, as they all use similar parts from other manufacturers for many components, including the compressor and electronics. What does differ between manufacturers is the warranty and service, controls, and pool automation communication.

Heat Pump Selection Considerations

Things you need to consider in choosing a heat pump are:

• Warranty and Support - many companies that sell heat pumps do not service them. Inquire who will provide warranty service locally and after warranty service. Members have found they had orphan heat pumps, and no one locally could fix the problem. Any service that touches the refrigerant requires a technician with a Section 608 EPA Technician Certificate.
• BTU (Heat) Output for your size pool—the largest heat pumps put out 130,000 to 140,000 BTUs. A 140K heat pump typically requires a 240 volt/50 amp or 60 amp circuit, while a smaller heat pump may require a smaller electrical circuit.
  • Pentair has a Heat Pump Calculator to determine the appropriate size Heat Pump for your location. Pentair seems to do honest calculations based on the physics and efficiencies of each type of pump and energy source.
  • Raypak also has a Heat Pump Heater Sizing App.
  • Aquacal has a Heat Pump Sizing and Savings Calculator.
  • To get the most accurate cost comparison, change the default electric kwh, natural gas, and propane prices to the actual prices in your area.
• Automation Compatibility—If you have a pool automation panel, you want your heat pump to communicate with it. All heat pumps can be controlled by a 2-wire control. Some heaters can be controlled by RS-485 digital communications with the automation. RS-485 comm usually requires the automation and heat pump to be from the same manufacturer.
• Chilling capability—Some heat pumps can both heat and chill a pool. Chilling a pool using a heat pump may not be energy-efficient. Cooling A Pool discusses other methods to chill a pool. For automation to automatically switch between HEAT mode and CHILLER mode, RS-485 communication is required, and even then, it can be glitchy. Research this area carefully and ask on the Forum with your pool details if this is important to you.
• Operating Temperature Range—Check that the heat pump's low-temperature cutoff and BTU output in cooler conditions meet your needs.

Heat Pump Operation

Heat pumps operate by taking heat from the surrounding air and transferring it into the water. The warmer the air and the more humidity, the more latent heat is available for heating your pool. Depending on the size of the heat pump for your pool volume; the heat pump can raise your pool 1/2°F to 2°F per hour depending on air temperature, humidity, and water temperature.

For example, a 140,000 BTU heat pump can raise a 17,000 gallon pool about 1°F per hour. A smaller BTU heat pump will raise the temperature less, as will a larger pool.

The ideal or rated condition for the heat pump is 80°F air temperature, 80% relative humidity, and 80°F water temperature. As conditions decrease from 80/80/80, the heat pump performance will decrease.

For example, the Hayward HeatPro BTU output decreases by about 30% with 50°F air temperature, 80% relative humidity, and 63°F water temperature. Under those conditions, a 110K BTU HP puts out 75K BTUs, and a 138K HP puts out 82K BTUs.

Heat Pumps are best utilized to maintain a set water temperature; they are not intended to provide instant or fast heating. It is unreasonable to expect a heat pump to perform like a gas heater with a much higher BTU output and quicker response. Additionally, gas heaters are not dependent on environmental conditions.

Proper operation and use of a heat pump involve setting it at your desired temperature and leaving it with your pool pump running. Like your home HVAC unit, your heat pump will turn on and off automatically to maintain your desired temperature.

Operate your heat pump during the day to maximize the sun's energy. Your heat pump will still operate when the temperature drops at night, but the output will be decreased. However, if you have lower nighttime electrical costs, you may choose to operate your Heat Pump only when electrical costs are lower.

It is acceptable to shut the heat pump off and not use it for extended periods.

Using a pool cover with a heat pump will minimize the pool water's heat loss and reduce the heat pump runtime, saving your electrical bill.

When you need to heat your pool, you must plan accordingly. Depending on your pool temperature and environmental conditions, the heat pump may take days to heat your pool back to your desired temperature.

Heat Pump Design

A heat pump transfers heat from the outside air to the pool or spa water through an internal heat exchanger.

When the fan is turned on, warm air is drawn through the refrigerant-charged evaporator, turning the cold liquid refrigerant into a warm gas. The gas then flows through the compressor, where it is compressed, resulting in a much higher temperature.

The hot gas enters the heat exchanger, where the water extracts the heat. The pump pulls in cool pool water, which converts the hot gas back into a liquid refrigerant and starts the cycle over again.

Modern heat pumps use R-410A refrigerant. It is a non-ozone-depleting refrigerant that the EPA accepts.

Heat Pump Components

• Evaporator: As air passes through the evaporator, the refrigerant in the evaporator absorbs heat from the ambient air. The warmer the ambient air and the larger the evaporator's surface area, the more heat it can collect.
• Fan: The heat pump fan produces high-volume airflow. Adequate airflow is required to move warm air through the large evaporator.
• Compressor: The compressor compresses the refrigerant gas to a higher pressure, increasing the temperature.
• Heat Exchanger: As the final step in the heating process, the heat exchanger transfers the heat from the hot gas to the water. (Also known as a condenser.)
• Reversing Valve (for units with chiller ability): The reversing valve reverses the flow of the refrigerant, which results in transferring cold gas to the water, thus lowering the temperature.

Heat Pump Bypass and Maximum Flow Rate

We recommend all heaters have a Heater Bypass.

Check your Installation Manual for the maximum flow rate for your heat pump. Heat pumps typically have a maximum flow rate between 70 GPM and 120 GPM to prevent erosion of the heat exchanger. If you have a Variable Speed pump running at less than full speed you usually do not reach the flow limit. If you have a large pump running at high speed for spa jets you may exceed the flow limit and need to bypass some water.

Heat Pump Preventative Maintenance

Manufacturers recommend that you inspect your heat pump continually, especially after abnormal weather conditions. The following basic guidelines are suggested for your inspection:

1. Make sure the front of the unit is accessible for future service.
2. Keep the top and surrounding areas of the heat pump clear of all debris.
3. Keep all plants and shrubs trimmed and away from the heat pump.
4. Keep lawn sprinkler heads from spraying on the heat pump to prevent corrosion and damage.
5. If the unit is installed under a roof edge, install a gutter or diverter to prevent excessive water and debris from pouring into the unit.
6. Do not use a heat pump if any part has been underwater. Immediately call a qualified professional technician to inspect the heat pump and replace any part of the control system that has been submerged.
7. If your HP has a condensate drain:
   1. Visually inspect and clear the bottom drain ports of any debris that could clog them.
   2. Ensure that condensate water does not puddle inside the heat pump.
   3. Ensure that condensate run-off is adequately directed away from the equipment pad to keep it from undermining the pad.
8. Keep the airflow discharge and intake area clear of debris so the airflow through the heat pump is not restricted. The cooler discharge air should not accumulate and be drawn into the intake coils.
9. Keep the air coil clean of dirt and debris. It is recommended to clean your air coil once a year by flushing it with compressed air or hosing it off with a garden hose.
10. Care should be taken not to bend the coil fins as this will restrict the airflow and lower your heat pump performance. Compressed air can also damage the heat pump coil. DO NOT USE A PRESSURE CLEANER ON THE UNIT.

Common Heat Pump Problems

Always check the Troubleshooting section in the Heat Pump Installation Manual on the manufacturers' website.

Compressor Not Running

The most common problem is that the fan at the top of the heat pump is turning, but you are not getting heat. The lack of heat is because the compressor is not running. The usual cause is a failed compressor start capacitor.

Another reason for this is a failed contactor that powers the compressor. Other less likely reasons are the compressor failing or a lack of refrigerant.

You check if the compressor is running by checking the amp draw using a clamp on ammeter.

The capacitor is circled in red, and the contactor is circled in green in the picture below from a Pentair UltraTemp heat pump:

Heat Pump Capacitor Replacement

Replacing a heat pump capacitor can be a DIY job if you are comfortable working around high voltages and follow proper safety procedures. The capacitor is a $20 part, and the service call can be $100 - $150. You can find YouTube videos on the process by searching for "heat pump capacitor replacement."

First, you must remove the power from the heat pump by pulling out the disconnect, which should be near the heat pump. Then, you can unscrew the side panels to find the capacitor. Note that the capacitor holds a charge and stores high voltage; even with the power disconnected, it can seriously shock you.

Wear glasses and gloves, take a picture, and note where wires go. Then disconnect the old one using long-nose insulated pliers and discharge the capacitor with a jumper wire or screwdriver across all terminals. Put a rag or towel over the capacitor since it can explode—not often, but often enough.

Many multimeters can test a capacitor.

Replace the capacitor with one of the exact uF specification and voltage.

Heat Pump Contactor Replacement

You will find YouTube videos on the process by searching "heat pump contactor replacement."

5 Minute Compressor Safety Delay

Note that heat pumps have a 5-minute safety delay between cycling the compressor. So, it may take 5 minutes after heat is requested for the compressor to turn on and heat to be generated.

Fan Not Turning

Check the HP circuit breaker if the fan on top of the heat pump is not turning. Obviously, check that the HP is turned on and that the set temperature is greater than the water temperature. The fan motor may have failed if there is electrical power and the HP is on.

Refrigerant Level

Heat pumps need the correct refrigerant level. It is common for refrigerant to leak out over time and eventually trigger an error. Low refrigerant can trigger low-pressure or high-pressure error codes. Servicing the refrigerant requires a technician with a Section 608 EPA Technician Certificate, proper test gauges, and tools.

NO FLOW Errors

Heat pumps have a minimum flow rate, typically 30GPM, needed to engage the Water Pressure Switch.

NO FLOW errors are often caused by a variable speed pump set at too low of a speed or a dirty filter. The first thing to do if you get a LOW FLOW error is to clean your filter. If the problem clears and then reoccurs, you may have algae in the water clogging the filter. Even clear water can have algae that clog the filter. See if your water passes the Overnight FC Loss Test, and if not, then you need to follow our SLAM Process.

Low Outlet Water Temperature

Heat pumps generate heat slowly. Depending on environmental conditions and water flow rate, the inlet water temperature and the outlet water temperature may not be very different. The heat pump puts out a fixed amount of heat (BTUs), and the outlet temperature varies by flow rate. A slower flow rate gives water more time in the heater to absorb the BTUs. However, at a slow or fast flow rate, the same amount of heat gets into the pool.

The table below shows the expected temperature rise for different BTU heat pumps at different flow rates:

Outlet Temperature Rise in F

	80K	110K	120K	140K
30GPM	5	7	8	9
40GPM	4	6	6	7
50GPM	3	4	5	5
60GPM	3	4	4	5
70GPM	2	3	3	4