For a superinsulated house, with low cooling load in summer but with the occasional need for dehumidification, it would appear on the surface that Climatemaster's Climadry option would be an ideal fit. It would provide dehumidification without overcooling. When I look on their site for details about Climadry, I see their note that it should not be installed on an open loop system or on any system without antifreeze. I would interpret this to mean Climadry should not be specified for an installation with a Standing Column Well design (SCW). I haven't found anything explaining the restriction, and I can only guess that since the internal water loop within the unit that circulates temperature-controlled water through the Climadry coil uses water that would be returning to the well (receiving heat in A/C mode), then in winter (heating mode) this water could conceivably be overchilled, depending on how everything is plumbed. All I have found is the small diagram showing the "COAX" exchanger with the internal water loop on one side and "refrigerant" on the other side. I would assume that the regrigerant would be downstream of the compressor, hot vapor, so that it has some heat to dump into the water. Is the COAX exchanger the same one that is there without Climadry, to absorb heat from well water (cooling mode) or providing heat (heating mode)? Bottom line question: does SCW design preclude Climadry? If so, what option is there for dehumidification without overcooling?

A dehumidifier? If you don't need any cooling, then geothermal doesn't buy you anything (because you have no waste heat to dispose of).

The problem is common with any oversized A/C system. The system shortcycles, reaching the thermostat setting before it's run long enough to dehumidify the air, leaving the inside of the house cool and clammy. A GSHP offers A/C as a sort of freebie on a system sized for heating in winter, so in heating climates, with the system sized for the heat load, the thing winds up often oversized for summer cooling load. Add to the equation a superinsulated house designed for minimal heat loss or gain, and very tight to help achieve that, and the resulting need for mechanical ventilation, which could be bringing in very humid outside air, and there is a problem. Climatemaster addresses this situation with Climadry, so the cooled and dehumidified air passing past the evaporator coil can be reheated, allowing the system to achieve dehumidification without overchilling the house.

Does anyone know how Climadry is plumbed into the system?

Meanwhile, it's back to Googling on it. I would think the answer is out there, and that I just haven't been looking in the right place.

Perhaps in the summer, they cool the water below 32F to maximize dehumidification with a water/air heat exchanger. Obviously there isn't generally a problem with running SCW or open loop GSHPs in the Winter.

Here are some key points: ClimaDry® simply diverts condenser water through a water-to-air coil that is placed after the evaporator coil. If condenser water is not warm enough, the internal “run-around” loop increases the water temperature with each pass through the condenser coil. All water system eliminates refrigeration circuit modifications (same refrigeration circuit as units without ClimaDry®)

DickRussell,

http://www.climatemaster.com/share/Res_All_Products_Bryant/Section_18_WholeHouseDehumid.pdf

Is a link to Bryant's geothermal Whole House Dehumidification: Application, Operation and Maintenance. It is the same as Climadry. There, you may find a couple of reasons why a closed loop with antifreeze is recommended for this application.

Regards,

Masoud

> Perhaps in the summer, they cool the water below 32F to maximize dehumidification

Looks like they go down to 20F.

I already saw that document, although not the Bryant version, virtually the same thing. How it works and is controlled is explained adequately, but there is no explanation of why antifreeze protection is required. I can't imagine any situation in cooling mode when the internal water loop would need freeze protection, as that water would be receiving heat when the unit is running. Presumably there is some plausible scenario in heating mode, when heat is being absorbed from the ground water loop, when freeze protection is required. For a SCW design, the flow of water from the well must be adequate for the unit size so as to keep the water from being overcooled, and the well may need provision for bleed to prevent excessive lowering of water return temperature. So where does the need for antifreeze protection come from, effectively precluding the use of Climadry with a SCW design?

Maybe I'll have to get a standalone dehumidifier for the back end of the heat pump unit. It seems like a shame if I can't use something so good in principle but somehow requires a closed loop/antifreeze water side.

Climadry should not be used on a SCW, Because you need to have antifreeze in the loop. It does not have to do with heating mode, You need the antifreeze for cooling with reheat mode (dehumid mode) . The Climadry(air) coil is directly next to the refrig(air) coil which can operate well below the freezing point of water. So the first air coil can freeze the second if it has no antifreeze. IF you have a SCW or any other ground water system, you need a seperate dehumidifier. And yes the COAX and refrig circuit is the same with or without Climadry

I see it - when the system is operating in cooling mode (no reheat), fresh water in the re-heat exchanger would freeze. Possibly a drain down system or air bypass could prevent that.

Question, then. If the air off the evaporator is subfreezing, then humidity is coming out as frost, and air below the ice point is going out to the duct work, causing condensation on the outer surface of the duct within wall and ceiling cavities. This also would give very uncomfortably cold air out of the registers. The temperature inside the evaporator coil is determined by the vapor pressure curve of the refrigerant and the evaporation pressure, and yes, depending on the tradeoff between coil area/expense and temperature difference driving the heat transfer the inside temperature could well be subfreezing.That would be why there is a minimum air flow required for proper operation, to provide sufficiently high outside film and bulk air temperatures so as to avoid frost and excessively cold air to the duct. I would think that proper design keeps the air from getting that cold in a residential system and therefore avoid any possibility of freezing the water in the Climadry coil. I'm not saying the explanation provided by heatoftheearth is incorrect, only that I don't totally follow the reasoning.

How low a temperature you need to run the coil at depends on how low you want to go humidity wise. But I agree that limiting evaporator coil exiting air temp to > 32F to avoid freezing the reheat coil seems like a reasonable and simple option.

I am going to disagree. I believe Climatemaster does not want the Climadry option installed on an open system because of the EWT. The Climadry option (when energized) sends the water after Coax to a separate reheat air coil. So if the EWT is 70° and in cooling mode the LWT is say 80°. That 80° water is used to reheat the air. If you are using well water then the EWT may be 55°. Then the LWT would be around 65°. You are not going to get much reheat from 65° water.

That's why it has a valve to allow bypass of the loop - to increase the temp.

I agree but with lower EWT (around 55) you will most likely over cool the space because not enough reheat is available.

The valve prevents the lower EWT - if necessary, it will completely remove the ground loop (or well) from the circuit. So low EWT simply won't happen.

FWIW here is a direct quote from Climadry Applications Guide, June 2009.

"ClimaDry Application Considerations ...

Unlike most hot gas reheat options, the ClimaDry option
will operate over a wide range of EWTs. Special flow
regulation (water regulating valve) is not required for low
EWT conditions. Temporary, slight overcooling of the space
may result on rare occasions with ground loop (geothermal)
systems during extremely low EWT conditions. Since
dehumidification is generally only required in cooling, most
ground loop systems will not experience these conditions."

In an earlier version of this document "extremely low EWT" was defined as EWT < 55˚ F.

Regards,

Masoud

I did see that Climatemaster does offer "Climadry II" in their "TL" models (Tranquility Large), which are apparently much larger than the 2-3 ton units at the low end. In this document:
http://www.climatemaster.com/downloads/97B0087N01.pdf
there is no mention of not using it in open loop systems or those without antifreeze. This leaves me wondering if not allowing its use without antifreeze in the smaller units is a matter of geometry/spatial arrangement within the cabinet of the smaller units. That in turn leaves me wondering if they may be working on reconfiguring the layout for future removal of that restriction. I guess only they would know.

Ok, I found a CM number for customer service, spoke with a tech guy about why Climadry on the smaller units had to have antifreeze. Apparently it's a matter of proximity between coils, about a half inch. Under some circumstances in cooling mode, like near loss of air flow, there can be ice formation on the evaporator, with bridging over the gap to the water coil, and the possibility of freezing it if the circulation through it is stopped. He said that even with the TL models, with a larger space between coils, the use of antifreeze in the loop still is suggested. The solution to the problem he agreed was more space between coils, but that would mean a larger cabinet, and according to him nobody wants a larger box. Nice fellow, easy to talk with, quite willing to explain things to me. Much appreciated.

IMO, no matter what spacing you use, blowing < 32F air through a coil containing non-circulating fresh water is a problem.

Either drain it (which might be difficult) or prevent < 32F operation when there is no flow through the reheat coil (ie, no reheat, only AC occurring). Or just use standalone dehumidifiers.

I am pretty sure that there is no air blowing though a coil containing water. The water is in a water to refrigerant coaxial coil. The air blows through a coil containing refrigerant.