Heat Pump COP and Low Temp Lock Out

04/18/24 • 56 min

This episode of the HVAC School Live Stream covers the key concepts around heat pump efficiency and understanding the coefficient of performance (COP). Eric Kaiser from TruTech Tools and Jim Fultz from White-Rodgers provide valuable insights into how heat pumps operate and how to optimize their performance, especially in colder weather conditions.

The discussion begins by exploring the COP of heat pumps and how it compares to the efficiency of electric resistance heat. A COP above 1 means the heat pump is delivering more heat for the same amount of energy input compared to electric resistance heat. Many homeowners mistakenly believe they should switch to emergency heat once the outdoor temperature drops, thinking the heat pump is no longer efficient. However, even at very low outdoor temperatures, a well-designed heat pump can still operate with a COP above 1, making it a more cost-effective heating option than emergency heat.

The conversation then delves into the concept of the thermal balance point, which is the outdoor temperature at which the heat pump can no longer meet the heating load of the home. The guests discuss how to calculate this balance point and how to set up controls to optimize the use of the heat pump and any supplemental heating sources, such as electric resistance heat or a gas furnace in a dual-fuel system. They emphasize the importance of proper air distribution and avoiding blowing cold air directly on the occupants, which can be a common complaint with heat pumps.

Key Topics Covered:

Coefficient of Performance (COP) and how it compares to electric resistance heat
Efficiency of heat pumps at low outdoor temperatures
Thermal balance point and how to calculate it
Optimizing control settings to balance heat pump and auxiliary heat usage
Importance of proper air distribution and avoiding blowing cold air directly on occupants
Considerations for dual-fuel systems with both a heat pump and a gas furnace
Best practices for programming thermostats and control systems to ensure optimal performance and comfort

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.”

Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.

Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Key Topics Covered:

Coefficient of Performance (COP) and how it compares to electric resistance heat
Efficiency of heat pumps at low outdoor temperatures
Thermal balance point and how to calculate it
Optimizing control settings to balance heat pump and auxiliary heat usage
Importance of proper air distribution and avoiding blowing cold air directly on occupants
Considerations for dual-fuel systems with both a heat pump and a gas furnace
Best practices for programming thermostats and control systems to ensure optimal performance and comfort

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.”

Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.

Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Previous Episode

Motor Protection Types - Short #192

In this short podcast episode, Bryan talks about motor protection types, including overloads.

The most common overload we see in residential HVAC is a built-in thermal overload, which is usually a bimetallic disk that flexes in response to heat (such as from a locked condition, electrical problem, or simply running hot) and opens the circuit. The two metals have different expansion and contraction rates, which causes the flexing; they will return to their original position once the motor cools down. In some cases, these can fail when they open and close too often; they are not designed for switching duty. Many circuit breakers have a similar thermal design and may be prone to nuisance tripping in the summer.

A lot of commercial motors rely on external overloads; some are even built into the electrical box rather than the compressor. These external magnetic overloads are often integrated into the contactor, which turns the motor on and off; this type of contactor is called a starter. These starters may have adjustable overload settings based on current, not just temperature (which may also respond to nuisance sources of heat and require a cooldown period). Some circuit breakers also trip magnetically and are less likely to be affected by temperature.

Thermistor-based overloads usually consist of a PTC (positive temperature coefficient) resistor; as temperature goes up, resistance goes up, which can take a motor winding out of the circuit. NTCs are in separate parallel circuits with relays; as the resistance decreases, it pulls in a coil that opens the circuit.

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.”

Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.

Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

Next Episode

EEV Types - Short #193

In this short podcast episode, Bryan explains electronic expansion valve (EEV) types. EEVs perform the same function as TXVs, but they operate electronically, not mechanically.

The EEV makes sure that the evaporator is full of the right amount of refrigerant at saturation; it doesn't just affect evaporator pressure. We don't want high superheat (due to inefficiency), and we don't want zero superheat (due to the risk of compressor failure).

EEVs commonly have a stepper motor with a set of discrete settings depending on how many rotations the motor has made. It can be fully open or fully closed, and the number of rotations can set the valve at any value between fully open and fully closed; it's open or closed by a specific percentage. Instead of a bulb and external equalizer, a pressure transducer and temperature sensor report to the controller and give the controller the data it needs to open or close the EEV to maintain a specific superheat.

Pulse-width modulation (PWM) allows an EEV to open and close rapidly. Unlike a stepper motor, PWM solenoids make an EEV stay fully open or fully closed for a specific percentage of time. It receives pressure information from a pressure transducer and temperature information from a thermistor or thermocouple.

As with a TXV, you would look at superheat and pressures to make sure the EEVs are operating correctly.

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.”

Subscribe to our YouTube channel at https://www.youtube.com/@HVACS.

Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).

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