Frequently Asked Questions:
Please refer to Heat Pump Water Heaters for Commercial Applications.
If the largest overcurrent protection is a Self-Protected Combination Motor Controller (MSP or MPCB) the largest overcurrent protection is 100% of the largest load. This may result in a MOCP equal to the Total Panel Ampacity (FLA), rounded down. Calculated according to UL 508a 32.3.1
To learn more please see Explanation of UL and Electrical Terms.pdf
Is there any advantage to multi-pass over single pass? When should I use series storage over parallel?
Stratified, Single Pass Storage vs Mixed, Multi-Pass Storage:
The only advantage we have found in a multi-pass system is the response from the contractor when reviewing the drawings. Single-Pass systems are not often understood at first glance because contractors are typically used to installing boiler systems in multi-pass configuration.
Stratified storage carries the potential of increasing storage capacity by over 500%. You can extract a lot more BTU’s out of stratified storage because the majority of your storage system can drop down to 50°F. While supplying 140°F water to the mixing valve. Since your entire tank temperature is equal to your delivery temperature in mixed storage, your minimum tank temperature can only drop to about 120°F before you start to deliver unacceptable water temperatures to the building.
Stratified Storage in Parallel vs Series:
There are two things to consider when choosing between storage in parallel or series:
- In-Series tanks will have a higher effective storage capacity because the stratification layer is only in one tank. That means all of the tanks downstream are 100% full of 140°F water.
- Each tank in series will see the full building DHW flow*. If two tanks are in parallel, each tank connection will only see half the building’s DHW flow. This may save on piping and custom tank connections.
*The flow through the tanks is calculated as: (tempered DHW flow) x (Hot water ratio between tempered and storage temperatures). For example, 10gpm max building demand @ 120°F will be a mixture of 2.2 gallons of 50°F water and 7.8 gallons of 140°F water. That means each tank connection in series will see a max flow rate of 7.8 gpm. If there are three tanks in parallel, each tank connection will see 2.6 gpm flow.
Here is an overview of the VFD operation:
As the quality of the heat to the evaporator source improves seasonally, the total Btu/hr. output of the heat pump improves.
The sizing of the heat pump array should be designed for the lowest quality heat the evaporator source will experience seasonally.
Adding a VFD to the compressor allows slower compressor operating speeds, resulting in lower total BTU/hr. output of the heat pump, lower energy usage and an improved COP.
With improved evaporator source heat, the heat pump array performance can be reduced to the original design output, by either reducing the number of units active in the array, or slowing the compressor speeds with a VFD across all or selected units in the array.
A combination of a reduced number of units in the array and reduced compressor speeds may be utilized to maximize the efficiency of the system.
As source temperature increases, power consumption and heating capacity increase. Source temperature affects heating capacity more heavily than it affects power consumption. Since COP is a ratio between heating capacity and power consumption, a higher source temperature results in a higher COP.
As entering water temperature increases, refrigerant pressure increases. The compressor is forced to work harder, which increases power consumption while decreasing heating capacity. As a result, higher entering water temperature yields a lower COP, while lower entering water temperature yields a higher COP.