Is a hot pre-heat tank and desuperheater LWT (125 degrees) a bad thing for a 3 ton horizontal loop Tranquility 27? It has been 12 degrees outside, and the heat pump running nonstop all day in 1st stage to maintain 70. Regards, Masoud

If you are asking about turning off your desuperheater to put more heat into the house, then the answer is yes but not much. By turning off the desuperheater you will get about 3000 more BTUh into your house.

Thank you. I was concerned about high water temp. Is it an indication of overworking the system? Dewayne, in one of your posts you indicted that a closed loop system should not run more than 90% of the time.
Regards, Masoud

The hot water temp is not a problem for the heat pump.

I think that the 90% number is referring to the design practice of sizing a heat pump and loop to take care of 90% of the load and letting strip heat make up the 10%.

I don't know of any problems created by running full time. Others might know more about this than me.


Have you thought about letting the unit go to second stage so it can reach set point and have a rest?

Thank you Dewayne. Yes, I can make it go to 2nd stage with supervision (manually rising the set point). But, then it starts in 1st stage again. With my thermostat automatic 2nd stage does not begin unless the room temp falls at least 2 degrees below set point. I'm sorry for misunderstanding about 90% run time.
Regards, Masoud

I know of no issues with long run times, especially in low stage. Long run times increase efficiency and, often, comfort. Do you find you house to be comfortable and evenly heated?

The 125 preheat tank means you are getting close to if not all of your domestic hot water made by the desuper - a significant bonus.

Where are you and what is the design low outdoor temp for your system?

Thank you engineer. The house is heated evenly with one zone, except when the fireplace is on. Then the back of the house loses 3 degrees. I am in SE Michigan. The winter design is -5 degrees. It seems that at current EWT, with outside temp in low teens, 1st stage is at its limit.
Regards, Masoud

Excellent!

I'm guessing the fireplace is kinda near the thermostat and fools it into cutting out too early for the back of the house.

That 1st stage gets you into the low teens suggests high stage will carry you right down to design temperature, with plenty of hot water to boot, unless loop temps fall appreciably.

One observation I meant to make earlier is that as EWT and preheat tank temps rise, the proportion of total heat going to hot water instead of your rooms, falls. That's good, since the very long run times come with decreasing outdoor temps and increased space heating loads. Desupers divert approximately 10 % of system heat, but the specification data assumes moderate desuper EWTs, in the case of WF, Envision, 90 F. At 125 the diversion is probably more like 5% or even less.

Masoud,

Just curious, what is your EWT?

Dewayne and Engineer:
Thank you for answering my question. Dewayne EWT was 43.6 degrees today. It has been a cold December in Michigan, around 15 degrees below normal. These are temps we normally get from mid Jan to mid Feb. The early low temps now will depress EWT later in Feb, when it can still bee very cold.
Regards, Masoud

Masoud, that's not bad our low EWT in Green Bay, WI is 38.8 already, definetly a cold year so far...

Masoud has a horizontal loop system, closed I assume. Brock, is your's also horizontal and closed?

Curious if those with vertical loops are also seeing descending EWTs earlier in the heating season!

Yup, horizontal closed (adjusted my profile), besides the radiant geothermal I have used 8 therms in the natural gas furnace this fall, I only seem to need the gas when it's really windy and below about 10F.