Heat Pump Water Heater Design Considerations

Introduction

As more projects move toward being “all electric” the topic of heat pump water heaters (HPWH) is often discussed. Being aware of the design considerations will help with the installation and use of the heat pump water heaters. It is possible to save money when using a heat pump water heater.

Most end users and designers expect the following of HPWHs: they won’t be noticed, using a HPWH will save money, and hot water will be available when it is needed.

Heat Pump Water Heaters are likely to produce noise and cold air

• HPWH have a noise level of 40-60 decibels.
  • Noise from quieter models would be similar to light traffic or a refrigerator.
  • Noise from louder models would be similar to conversational speech or an outdoor air conditioner.
• HPWH located in a closet will require airflow into and out of the closet. This is often provided by using two louvers from the closet into the living space.
• HPWH take heat from the air and delivers cold air back to the space (45-50 degrees F. which is the similar to the air temperature that an air conditioner delivers to a room). The discharged air needs to be directed to a space that isn’t temperature sensitive.

It is possible to save money while using a HPWH

• HPWHs use less electricity than a conventional electric water heater when in heat pump mode.
• A HPWH will initially cost up to 2-3 times as much as an electric water heater that is the same size. Note that equipment rebates are often available from utility companies.
• The air conditioner / heating unit serving the living area will often be larger (increased equipment cost) to provide the needed heat to the HPWH (heat pumps only move heat and aren’t capable of generating or creating heat).

Hot water available from a Heat Pump Water Heater

• The tank of a HPWH has basically the same size tank as an electric water heater.
• When all the hot water in a tank type water heater is used (tank now has cold water in it being heated) the time required to re-heat the tank are as follows:
  • HPWH will take up to 12-hours to heat the tank (while in heat pump mode).
  • Electric water heater will take 1-2 hours to heat the tank.
  • Gas water heater will take 30-minutes to an hour to heat the tank.
• A HPWH will often switch to all electric mode (not using the heat pump) during periods of high hot water demand. Basically, the water heater will perform as an electric water heater without the money savings of the heat pump function.

Conclusion

It is possible to save money when using a heat pump water heater, but it is necessary to address all the design considerations. Using a heat pump water heater may not be the best choice for all projects. When working with our design teams at Royal Engineering, we can help to advise the best fit for your project.