The WF Envision system has the following feature per the installation manual I have:

"Note: Under certain conditions, Envision dual capacity units operate with very low refrigerant discharge temperatures,
producing little or no water heating capability. This scenario occurs when the unit is operating with cold entering source
water (loop or well). Allowing the desuperheater pump to operate during these conditions actually removes heat from the
DHW circulating through the unit. To overcome this, Envision unit microprocessors have been programmed to disengage
the desuperheater pump during such conditions. (During low capacity cooling operation, the pump will operate only if
the DHW temperature entering the unit is less than the liquid line temperature plus 35º F. During high capacity cooling
operation, the pump will operate only if the DHW temperature is less than the liquid line temperature plus 60º F.) Using
a preheat tank, as shown in Figure 12, will maximize desuperheater capabilities."

I have not witnessed our DSH unit not producing hot water (by feeling the in/out DSH lines) when the geothermal system is running.
Edit - to clarify, and remove the double negative, I always observe our DSH producing hot water whenever our geothermal system is running.

So WF seems to have the same issue. CM does not turn on until the compressor discharge is at least 125, Wf seems to have this solved better by monitoring the delta T between Source EWT and DHW temp. I have a Synergy 3 D in my house, and it was stealing temps form the DHW tank, so I had to have a buffer tank, that way lowering my DHW temp, which solved the issue. It is an early R410 unit. May be they realized that this is a problem and programmed this algorithm into the circuit board. However, buffer tank does not get above 90 at about 65 Source EWT.

Could Waterfurnace jump in here and provide more information about the desuperheater operation with R-410 units. Many people have issues and it would help to get to the bottom of this. What temps can someone expect to be generated in lets say Northeastern Climate? Is it even worth putting DSHs in?
What is the efficiency of a 2 tank versus 1 tank design? etc...

Posted By docjenser on 18 Aug 2010 02:19 PM
Could Waterfurnace jump in here and provide more information about the desuperheater operation with R-410 units. Many people have issues and it would help to get to the bottom of this. What temps can someone expect to be generated in lets say Northeastern Climate? Is it even worth putting DSHs in?
What is the efficiency of a 2 tank versus 1 tank design? etc...

You pretty munch hit it on the head there. R 22 did not have this issue because of higher discharge temps. R 410A is more efficient with lower discharge temps which unfortunately means less DSH in cooling mode with lower EWT. As they say you can't have your cake and eat it too. Manufacturers were not aware of this issue when R 410A was first used until customer complaints brought it to their attention. If the condensing temperature is low so goes the discharge temperature with R 410A and there's not much you can do about that. Ever put you hand on the discharge line in cooling with 65F EWT? I remember burning my hand/arm many a time on R 22 systems that taught me not to do that. It might be good exercise to monitor EWT and discharge temps in cooling mode to get familiar R 410A. Of course in heating mode we are not working with low condensing temps.

Come on Waterfurnace!
You guys know much more about this issue than we do. Would be great if you could provide us with as much background info as possible.

According to Heat Controller, Inc, maker of GeoMax 2, the DSH pump comes on immediately with the geothermal compressors, and will cut out (basically a thermostatic switch inline with the DSH circulation pump) once the incoming water from the storage tank reaches 125 F.

My fun is that with a single 40 gallon tank that's also heated with an AirTap, I have to make sure the AirTap doesn't heat the water above 125, otherwise, the DSH will never activate! Guess that's why people have buffer tanks?

The GeoMax manual that I looked at gave a choice of 125 or 150f that was selectable. Definitely scald territory at 150f, so beware.

Doc, I was holding of responding in the hope WF would answer your question directly. The WF Envision Residential Specification Catalog that I have a pdf of gives lots of figures. Let me know if you want me to PM (or email) you what I have if you don't see it online.

Posted By stuart.wyss on 20 Aug 2010 06:25 PM
According to Heat Controller, Inc, maker of GeoMax 2, the DSH pump comes on immediately with the geothermal compressors, and will cut out (basically a thermostatic switch inline with the DSH circulation pump) once the incoming water from the storage tank reaches 125 F.

My fun is that with a single 40 gallon tank that's also heated with an AirTap, I have to make sure the AirTap doesn't heat the water above 125, otherwise, the DSH will never activate! Guess that's why people have buffer tanks?

Heatcontroller is made by Climatemaster All the manufactures have the same issue! You can set it to 150 degrees or 125 degrees max temp, however, the DHW pump will not turn on in cooling mode because the discharge temperature is not "sufficiently" above the water temperature. No problem in heating mode. Geomax2 Install Manual: "Installation The HWG is controlled by two sensors and a microprocessor control. One sensor is located on the compressor discharge line to sense the discharge refrigerant temperature. The other sensor is located on the HWG heat exchanger’s “Water In” line to sense the potable water temperature." "The microprocessor control monitors the refrigerant and water temperatures to determine when to operate the HWG. The HWG will operate any time the refrigerant temperature is sufficiently above the water temperature. Once the HWG has satisfied the water heating demand during a heat pump run cycle, the controller will cycle the pump at regular Intervals to determine if an additional HWG cycle can be utilized. The microprocessor control Includes 3 DIP switches, SW10 (HWG PUMP TEST), SW11 (HWG TEMP), and SW12 (HWG STATUS)."

It's the way it works and the way it is supposed to work. I don't think there is an "issue" to address.

I don't have that in my manual (!), but the schematic definitely shows TWO thermostatic switches, but they seem to be in series with the HWG pump. Anyone have an electronic GeoMax manual handy?

G_ogle "heat controller geomax 2 installation manual". It was the second link when I just tried it.
I can email you what I downloaded if you want. PM me your email.

Posted By stuart.wyss on 21 Aug 2010 04:14 PM
I don't have that in my manual (!), but the schematic definitely shows TWO thermostatic switches, but they seem to be in series with the HWG pump. Anyone have an electronic GeoMax manual handy?

http://www.century-hvac.com/index.php?option=com_rubberdoc&view=doc&id=92&format=raw

Selectable 125˚ / 150˚ HWG temp limits is a new control feature. Older models including my Tranquility 27 (built Sep 2008) and some units manufactured in 2009, based on their documents, only have a fixed 125˚ limit, factory set on entering water pipe to DSH.

Regards,

Masoud

Posted By jonr on 21 Aug 2010 04:02 PM
It's the way it works and the way it is supposed to work. I don't think there is an "issue" to address.

It is an issue when in many places or with certain designs the DSH never turns on in the summer. If you have an open system in the northeast, the DSH will not turn on in the summer. I have two customers with closed loops where the DSH has not turned on in A/C mode this year since Heatcontroller a year ago put a switch in the units which does not turn on the DSH pump unless the compressor exhaust discharge temp is 125 F. Or my own unit, which was stealing heat from the DHW tank and putting the heat into the ground. Or all the other customers where the buffer tank does not get above 90 F in A/C mode. It might not be an issue for you, but for people like me who pride themselves to build the most efficient system for our customers, it is an issue. We must set expectations correctly, and come through on our promises. Take for example the misleading statement from the heatcontroller installation manual, that the HWG is active throughout the year. "The HWG is active throughout the year, providing virtually free hot water when the heat pump operates in the cooling mode or hot water at the COP of the heat pump during operation in the heating mode." It is not an issue for the marketing person who wrote this, and maybe not an issue for you,.... but if the DSH does not perform as promised, it is an issue for me and my customers. It would become an even bigger issue if I do not understand it and incorporate it into the design of the next system, or at least lower the expectations of our customers and tell them upfront what to expect. So I guess it not not a matter whether this is an issue or not, but for whom it is an issue. Apparently not for you, ...but certainly for me.

Posted By Masoud on 22 Aug 2010 12:30 AM
Selectable 125˚ / 150˚ HWG temp limits is a new control feature. Older models including my Tranquility 27 (built Sep 2008) and some units manufactured in 2009, based on their documents, only have a fixed 125˚ limit, factory set on entering water pipe to DSH.

Regards,

Masoud

May be down the road we get to select the radiant heat output temp in the same fashion....so we can finally get radiant baseboard retrofits to work like they do in Europe!

No doubt some marketing materials are wrong and should be corrected. But I wouldn't say "All the manufactures have the same issue!" or expect one manufacturer to comment on another's marketing claims.

Posted By jonr on 22 Aug 2010 08:52 AM
No doubt some marketing materials are wrong and should be corrected. But I wouldn't say "All the manufactures have the same issue!" or expect one manufacturer to comment on another's marketing claims.

Let m e try to explain it again: It is an inherent issue issue with R-410 in A/C mode, so every manufacturer has the same issue. And yes, I expect them to comment on it but they do not. They all try to solve it differently. First they found out that if the EWT is too low, there is some reverse heat transfer from the DHW tank to the refrigerant circuit. So they installed a switch which did not turn on the DSH pump unless the exhaust temp is above 125 F. Which meant that even buffer tanks were not pre-heated in A/C mode. So apparently waterfurnace and CM now uses a Delta T between tank temp and exhaust temp to allow the pump to turn on. We did not recognize it until some customers complaint that the DSH is not running. Then we started to monitor the DSH load lines and the buffer tanks (and everything else) with the WELserver. Then it took us quite a while to get a response out of Heatcontroller. We have installed Hydron, Waterfurnace and CM units, and yes, they all have the same issue. And yes, for us it is an issue. Most people here might not recognize it, but if you monitor the systems you find out pretty quickly.

Posted By docjenser on 22 Aug 2010 10:30 AM

Posted By jonr on 22 Aug 2010 08:52 AM
No doubt some marketing materials are wrong and should be corrected. But I wouldn't say "All the manufactures have the same issue!" or expect one manufacturer to comment on another's marketing claims.

Let m e try to explain it again: It is an inherent issue issue with R-410 in A/C mode, so every manufacturer has the same issue. And yes, I expect them to comment on it but they do not. They all try to solve it differently. First they found out that if the EWT is too low, there is some reverse heat transfer from the DHW tank to the refrigerant circuit. So they installed a switch which did not turn on the DSH pump unless the exhaust temp is above 125 F. Which meant that even buffer tanks were not pre-heated in A/C mode. So apparently waterfurnace and CM now uses a Delta T between tank temp and exhaust temp to allow the pump to turn on. We did not recognize it until some customers complaint that the DSH is not running. Then we started to monitor the DSH load lines and the buffer tanks (and everything else) with the WELserver. Then it took us quite a while to get a response out of Heatcontroller. We have installed Hydron, Waterfurnace and CM units, and yes, they all have the same issue. And yes, for us it is an issue. Most people here might not recognize it, but if you monitor the systems you find out pretty quickly.

Unfortunately this is part of the learning curve involved with geothermal all R 410A units will have low discharge temps in AC mode @ low condensing temps. You can bypass the low limit if you have a buffer tank and see what happens. Marketing hypes tend to get carried away sometimes so draw your own conclusions and learn from the experience.

So, if I have a single tank (40 gallon) and it's being heated by an AirTap, set at 120 F or thereabouts, and my GeoMax 2 (R410a coolant) is running, chances are the desuperheater is contributing very little to the hot water situation? I don't have a setting for 125/150F, mine's the older version of the circuit board). Hopefully, heat isn't being "stolen" from the tank and, I guess, put into the ground?

I'm depending on the accuracy of both the AirTap thermostat and the DSH circulator thermostatic switch to maintain an ideal balance.

Could not agree more. But part of a forum is to share the experience and be part of the learning curve, and given the comments earlier, not many people seemed to have been aware of it. However, manufacturers should be more forthcoming to update the field of the "issues", so we set expectations correctly with the customers or design around it.