Connection between GSHP and Zehnder’s ComfoFond-L
I wish to make a connection between the ground loop of a Ground Source Heat Pump and the air tempering unit of a Zehnder ERV ventilation system, the ComfoFond-L (which usually utilizes it’s own independent ground loop).
I believe that I remember reading about a project in Vermont, perhaps with a government associated housing project, that used ClimateMaster GSHPs and Zehnder ERVs in just this way.
Barry Stephens, formerly a representative at Zehnder but now working elsewhere, remembers such a project and indicates that Zehnder has pictures of the connection on file; he referred me back to Zehnder for further information. Several contacts at Zehnder were unfamiliar with the Vermont project and have been unable to provide information.
Does anyone at GBA, or any of the readers of GBA, remember such a project and perhaps the people involved; or, know of any way I can get information relating to it ?
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I don't know about the Vermont project, but I am planning on setting up a similar system this summer--using a flat-plate liquid-to-liquid heat exchanger to link my existing GSHP loops to a new water-to-air heat exchanger on the intake of a new Zehnder HRV system. I opted not to use the Zehnder tempering unit because I was going to need to design other parts of the system anyway, and it's easier and cheaper to do that from scratch than by trying to reverse engineer their system. And it also allows me to select my own pumps for extremely low electricity consumption.
The need for the water-water heat exchanger is that the glycol in my GSHP loops is very dilute, and would not be adequate for freeze protection in the intake airstream. So there will be a small loop of high-concentration glycol just running between the water-water heat exchanger and the water-air heat exchanger.
My expectation is that the main benefit will be dehumidification of ventilation air in the summer. I am planning to control it based on a dew point sensor, to run whenever the outdoor air dew point is high enough that I will get significant dehumidification, as well as using a temperature sensor in the winter to run it when the incoming air is cold enough to risk freezing up the HRV.
Charlie,
Sounds like an engineer's delight -- using lots of complicated equipment to save a relatively small amount of energy. But if anyone can design it and commission it and maintain it properly, it's you. Good luck.
Martin, thanks for the compliment and criticism, which is well taken, no pun intended. I am aware that the complexity is a major limitation, and that it is very unlikely to be useful to any future residents here. I am hoping that it provides a comfort benefit in the summer through lower humidity more than I am hoping for enough energy savings to justify it.
I also hope it will provide an example to others...probably primarily an example showing how much complexity is needed, to dissuade people from undertaking it when they shouldn't. But perhaps someday it could become a packaged product.
Ted, what climate are you in? Another limitation of this approach is that the benefits I expect are specific to my humid zone 6 climate. I should also note that my ground loop is oversized for my now better insulated house; it would be even harder to justify for a new installation, and would be limited to the non-dominant load season in an existing loop with marginal capacity.
I'm in northern CZ-4. New construction of a ranch style 2900sf home to commence within a couple months. I plan on using ClimateMaster Triology 45 Q-Mode 0930 GSHP (all three motors are variable speed) (also provides hot water all year using house air in the summer and ground source in the winter) which operates down to 9,000 BTUs at it's lowest speed. I am somewhat ambivalent about the air tempering unit as it will remove some of the load and possibly interfere with the optimum operation of the GSHP.
I have included a graph of my cooling load profile, attached below; it's yet to be confirmed by Manual J but matches a preliminary REMRATE analysis. The CTS + RTS labeled line is the expected cooling load over a 24 hour period on a peak summer design temperature day. My concern is that the the already low load (peak of about 9,500 Btu) will be lowered further, especially on all those non peak days, such that the GSHP will not dehumidify adequately (although the latent load should be lowered by the air tempering unit before it's presented to the GSHP). I think the GSHP would perform better with the higher load.
At this point I want to keep my options open and find out just exactly how the connection between the GSHP and the ComfoFond is made (the ComfoFond uses about 1.6GPH to operate)
I understand that this is probably not the best economic path to follow in my climate but my prime goal is COMFORT within economic reason.
Your opinion would be appreciated.