It varies among units and with loop temperature, but I'd say most units have a practical limit between 120 and 130F. Compressor durability is the limiting factor. Mine was originally listed as being capable of 130F, but between when I ordered it and it arrived the 130F points had been removed from the performance specs and a hard limit of 125F was specified. This was further revised to 120F or 115F depending on which section of the manual you look at. Last winter I limited my LWT to 120, so my buffer tank tended to stay between 105 and 115 or slightly higher in the coldest weather. At these temps the compressor discharge was over 220F, which is a concern according to Copeland, but the discharge temp limit on the heat pump is set at 275, so I wasn't anywhere near tripping the limits. I'm hoping Copeland's suggested limits are over-conservative and I'll get many years of life from the compressor.

In general, I believe R22 units have a slight advantage over R410 units due to lower discharge pressures and temps for a given condensing temperature. Also, units with larger heat exchangers on the hydronic side can produce higher temps. Looking at Copeland's spec sheets the compressor itself makes a big difference as some are more optimized for high condensing temps. Mine unfortunately is designed as a "pool heater" and is not capable of as high a condensing temperature as some.

The loop temperature will also have a big effect. Higher loop EWTs will give you lower compressor discharge temps so you should be able to safely run higher condensing temps.

Keep in mind that you'll have a temperature drop through your heat exchanger for your hot water, so that will knock another 5-10 degrees off depending on configuration (you are isolating your DHW from your radiant I hope!).

thanks Cnygeo,

Yes, we will use an indirect water heater and I'm thinking we may be able to use 110 deg water, so 120 LWT will probably be needed for that.

This will be an open loop, so 50 deg source water should be feasible. I have started to wonder if R-22 machines might be worth looking at as they often seem to list slightly higher water supply temps, and higher COPs in this range.

You have given me a new area to consider re the hydronic side heat exchanger. When you consider refrig temps as high as 220 degs, it does seem that different heat exchanger designs, i.e., increased heat exchanger size and/or efficiency could make a big difference in the max hydronic temp available.

Maybe this is the magic in the new Climate Master unit (Tranquility THW Water to Water) where 145 deg temps are promised, they don't use the standard coaxial heat exchanger, they use a brazed plate heat exchanger. That would be very interesting if this were the major reason for these higher water temps.

(large 5 meg spec catalog here http://www.climatemaster.com/downloads/RP812(2).pdf)

Cnygeo - what unit are you using?

I am surprised about the de super heater temps. Our Geo Comfort GWSR048 will hit 160F+ (when the sensor goes blank). I thought it was suppose to shut off at some point, about 130F, but it doesn't, just slowly keeps heating up. This isn't a problem because we have two tanks and the primary natural gas water heater is set for about 115F, but it will slow raise in temp when we use water from the pre heat tank.

So how is our DSH heating to such a high temp?

Brock,
As I understand it, your unit is a water to water HP with desuperheater.

Your desuperheater temp is VERY IMPRESSIVE!  Maybe there isn't a safety on that temp, you might want to add a high limit stat?

I see your system is used as a pool heater, so you may not know how high it will go in the "normal" water heating mode, I'd be curious to hear the hottest you've seen on normal water heating (not desuperheater). 

How do you like the unit overall, how long installed, any problems?

Yes it is water to water. The highest I have seen the out water was 130F and back in at 125F with a field temp of about 30F out and 35F back in. That was heating out hot tub when we only had one 125K heat exchanger, now that we have two heat exchangers in series and the pool has warmed up in spring I typically saw 115F out and 110F back in with the field side at 40F out and 45F back in.

The unit was installed 4 months ago (field was over a year ago now), so I am new to all of this. I really like it, it is much more quiet then I had thought it would be, honestly it is about the same as out big side by side fridge, although they set it on a 2 inch thick soft plastic pad thingy, I think that helps a lot with noise.

We have a horizontal loop field out in the side and back yard, 4 tons worth, 10 feet down, 8 feet wide, 250 feet long. Right now when the loop field is about 58F since we dump a lot of the cooling to the house.

Well, those water temps sound very good. 130 output with 35 EWT. 130 deg in the coldest weather should be good for our radiant heat system, normally will be more like 100 - 105 deg in milder weather... and we will have an open loop with close to 50 deg EWT. Glad to hear it's working out, this sounds encouraging for GeoComfort brand.