By Allen Hibner: November 27th, 2023 – It has been quite a while since I published a new blog article in this continuing ALL-ELECTRIC-Life series. My wife and I have been living happily in our ALL-ELECTRIC home for almost 1½ years now after we installed our heat pump dryer; our 4th and final heat pump unit. See: NOW…We’re Living the ALL-ELECTRIC-Life! We’ve also been enjoying our geothermal (ground source) heat pump system for 2½ years. It’s time to report on some of our exciting findings about these systems in this installment.
SECTION I - DESUPERHEATER 101 – What is it and why should you care? In this article you are about to learn more about an optional and somewhat arcane component of our WaterFurnace 7 Series geothermal HVAC system that is little known but that provides some big benefits. Here it is in a nutshell: When the 12-speed compressor in our WaterFurnace 7 series runs during the heating or cooling cycle, it produces some amount of waste heat. That’s unavoidable for an electric component that can draw close to 4,000 watts when running at its highest compressor speeds. A DESUPERHEATER unit recovers some/most of that waste heat to PRE-HEAT the water in a hot water heater tank, thus reducing the amount of electricity needed overall to heat water for our domestic use. It’s as simple as that! What follows here is a much “deeper-dive” into the details of how our own Desuperheater unit has been performing. Read on… I think you will be surprised!
Let’s begin with some images; WHAT does a Desuperheater heat exchanger look like and WHERE is it located in the cabinet of a WaterFurnace 7 Series geothermal HVAC unit?
OK, now that you have seen what it looks like and where it is located, how does it operate? This diagram does an excellent job tracing the flow of cold, warm and hot water through a Desuperheater assisted hot water pre-heating system. NOTE: Pre-heated water is supplied to the passive “Pre-heat” tank during BOTH the heating (winter) AND cooling (summer) cycles since the compressor, the source of the Desuperheater’s recaptured waste heat, is running during both cycles.
Even better, let’s take a look in the image that follows at that same flow of hot, warm and cold water TO/FROM the Desuperheater and throughout the hot water heating system IN MY OWN EQUIPMENT as it is currently installed:
Finally, in this last part of the Desuperheater 101 section, let’s take a look at the WaterFurnace’s heating/cooling cycles (see Figures 1A & 1B below) and where the Desuperheater unit fits into the flow of refrigerant and water to/from the unit’s air exchanger and geothermal ground loop.
Notice that the Desuperheater performs the SAME WAY in both the heating AND cooling cycles! The compressor first compresses and super heats the refrigerant. The Desuperheater heat exchange unit then removes some of the excess heat from the refrigerant and transfers it to the hot water heater system’s passive water tank. Because the WaterFurnace system must regulate the maximum temperature of the refrigerant when first compressed, any heat over the maximum allowed would be removed and WASTED if there was no Desuperheater. Instead, it is captured and recycled to pre-heat hot water. BRILLIANT! EFFICIENT!
ALSO NOTE: The MAGIC of this ground-source heat pump system is the REFRIGERANT REVERSING VALVE! If you follow the flow of refrigerant closely in the image above, you will notice that during the HEATING CYCLE the hot refrigerant flows into the WaterFurnace’s air heat exchanger after leaving the Desuperheater where cool air returning from the house is warmed up and sent back through the home’s duct work to heat the home. In the COOLING CYCLE the reversing valve directs the hot refrigerant into the ground loop system where the heat can be released into the ground and the refrigerant is cooled. BRILLIANT! CLEAN! GREEN! EFFICIENT!
SECTION II - DESUPERHEATER PERFORMANCE - How has our Desuperheater system performed so far?
Setting the Stage – Measuring the kWh's Used: In order to be able to measure how much electricity our hot water heater was using on a daily & monthly basis so that I could analyze how well the Desuperheater system was performing, I installed an Iammeter circuit monitoring device (see image below) and attached the leads to the 30 Amp Hot Water Heater circuit. I then recorded electricity usage data daily – summarized monthly - for the next 10 months.
Results – Data Analysis:
During the (4) winter months of December 2022 through March 2023, the AVERAGE amount of electricity used/month by the A.O. Smith heat pump hot water heater was 32.8 kWh/Month. The average runtime of the WaterFurnace 7 Series Geothermal system was 583.3 Hours/Month.
During the (4) summer months of June 2023 through September 2023, the AVERAGE amount of electricity used/month by the A.O. Smith heat pump hot water heater was 132.8 kWh/Month. The average runtime of the WaterFurnace 7 Series Geothermal system was 140.6 Hours/Month.
Our hot water heating system with the Desuperheater installed in it used on average 100 kWh/month LESS in the winter months as compared with the summer months – 4 times or 400% LESS ELECTRICITY/month because of the Desuperheater system!
Conclusions:
Clearly, when the WaterFurnace is running 19-20 hours/day in the winter months during heating season, a great deal of heat is being recovered by the Desuperheater and sent to the pre-heat water tank.
In the summer months during cooling season, the WaterFurnace runs 400% less than in winter (about 4.6 hours/day) – recovering much less heat through the Desuperheater that can be sent to the pre-heat tank.
As one would expect, the graph shows a very tight correlation or tracking between the WaterFurnace’s runtime hours and the total number of heating/cooling degree days. This makes a lot of sense.
Bottom line: I was quite surprised by these numbers actually. I did not initially expect such a large gap or “heat recovery gain” from having had our Desuperheater unit installed with our WaterFurnace 7 Series geothermal system. I’m very happy about these results! As prices for electricity inexorably rise in the coming years, we will be saving more and more dollars by having this system. Also, even though our family participates in Penfield’s “Penfield 100” CCA program and we power ALL of the devices in our ALL-ELECTRIC home with 100% renewable electricity, it still feels very rewarding both environmentally and financially to be able to use less electricity because of this Desuperheater system. The benefits of clean, green and environmentally sound electric heat pump HVAC technology are what will really help to propel all of us into a fossil-fuel-free-future. For the Hibner family, living in our now 100% all electric 1955 raised ranch Penfield home, that clean, green renewable future has already arrived!
Thanks so much for reading the articles and watching the videos in this continuing series. I hope they are helping you to consider going ALL-ELECTRIC for your own home heating and cooling system needs.
Again, as always, where can you obtain even more local assistance to explore air source and geothermal (ground-source) heat pumps? We have a phenomenal resource right here in the Rochester/Finger Lakes regional area. I strongly encourage you to visit AMPED GO ALL ELECTRIC to learn how to go ALL-ELECTRIC in your home.
