Just in case anyone is interested:

measured KWH, Gallons, and temperature change supply/return on our altherma for a full day yesterday.

-Water temps around 85 deg F.

-Outdoor Temp averaged 14 Degrees and the whole day was in the 11 to 16 degree range. 56 degree Days.

-We did see some "snow cake" as it was snowing HARD yesterday, which I think must reduce our output somewhat as it impedes airflow through the coils.

-Calculated heat load on the building is a bit shy of 33kBTUs/hr at a -4 deg F. outdoor design, or about 10,700 BTUs per degree Day.

-Total power draw of the 054 altherma and its backup heater for the 24 hour period: 36.5 KWH

-Total BTUs for the day were 258,772. Remember this was during a snowstorm, and we only had 3 people in the building. For the degree days we had, and our calculations, we'd expect to see 600,000 BTUs for the day. So at least on this day, our load is about 1/2 of what we calculated... And we calculate aggressively. I have to admit, this one takes me aback a bit. Makes me wonder if I'm missing something. Our warehouse level is about 64 average instead of 70, so that helps, but still.... no solar gain. Our infiltration calcs could be reduced but even if I eliminated infiltration entirely that's only half of this differential.

-Assuming we have real numbers though, our calculated COP for the day was 2.08 .

We'll let it run for more days and try a week long number next. since we do have a slab level, our numbers might shift depending on when the slab calls.

Still, pretty cool stuff. Monitoring rocks!

Slow poke. What are you using for your monitoring?

We are using Climate Automation Systems' "ENV" system, which is basically home automation hardware tied to a software package similar to a DDC control but a bit friendlier. Pretty cost effective too. Our shop was our first experience with the system and it was daunting at first, but we think we'll be using it significantly more often moving forward.

Alright, the numbers I posted above included backup usage which is straight electric. We haven't yet figured exactly how it determines when to use backup, but we are suspecting that it occurs during defrost periods.

Yesterday was sunny and much warmer, 20.1 average temperature for the full day, 49.9 degree days.

Unit produced 259,000 BTUs using a total of 31 KWH, 4.5 on the backup and 26.5 on the heat pump.

so again we used half the BTUs per degree day we expect to see, for one. COP for the heat pump itself is 2.7 for the day, and when backup usage is figured in, it goes down to a 2.45. With Current oil prices ($3.50/gallon) and electric (roughly 0.15/kwh) we only need to exceed a COP of 1.75 to run cheaper than oil.

Sensor Error! our readings show the return temp sensor was miscalibrated with the supply by 1.5 degrees.

What does that mean?

at outdoor temperature average of 20, we are actually seeing heat pump COP of about 3.5, 3.2 to 3.3 when you factor in backup usage! That's better.

BTU per DD for the building is still oscillating between 5000 and 7000/Day.

Yesterday's numbers (2/4/11): another sunny day.

20.3 Average outdoor temp
49.7 Degree Days
246,000 BTUs
19.3 KWH Heat Pump
2.3 KWH Backup Heater
3.62 Heat Pump Only COP
3.34 COP with Backup usage
4954 BTU/DD.

Do you have the Daikin hot water heater, too?

nope, just heating/cooling with it. our DHW load is pretty much non-existent.

we have continued tracking the COPs and so far, the lowest average outdoor temp WHILE OPERATING has been 8 degrees for a day... and under those conditions we're still over a combined heat pump/backup COP of 3.

the 2.7 we saw on the first days of logging appears to be the result of the very heavy snowfall we had on those days: it caked up the outdoor unit during the storm itself, which apparently cost us about half a COP. but immediately after the storm all the snow defrosted out, and we haven't been under a 3 COP yet.

That's astoundingly good air-source performance. Is 85F pretty much your peak water temp, or do you ever run it warmer?

85 is our design water temp. So far we seem to be about half a COP over the published numbers for the Altherma given 86 degree water and appropriate outdoor temps for our unit... pretty cool... which means at these lower outdoor temps if that trend held true we should be able to generate 113 degree water for roughly half a COP less... though under warmer outdoor conditions that differential can widen to 1 to 2 full COP.

I wish we had a couple more subzero nights... we made a mistake in our install that means we didn't get any good data a few weeks ago when it was really, really cold at night. ah well.

be careful what you wish for ;-)

Rob

After looking at this post and looking at the web site, this looks like a great solution for an ICF house we are building. (Still in the architects hands.) I was cosidering geo but architect said it it looked like overkill. In fact the architect thinks radiant may not be cost effective.

Friends in Austria us solar as a preheat, something we are very interested in, now I see on the Daikin site an actual recommendation for installation.

Home in Northern NY, 1600sf one level open floor plan, with basement.

I am most interested in the numbers, please keep up the post.

RRR

Rob

After looking at this post and looking at the web site, this looks like a great solution for an ICF house we are building. (Still in the architects hands.) I was cosidering geo but architect said it it looked like overkill. In fact the architect thinks radiant may not be cost effective.

Friends in Austria us solar as a preheat, something we are very interested in, now I see on the Daikin site an actual recommendation for installation.

Home in Northern NY, 1600sf one level open floor plan, with basement.

I am most interested in the numbers, please keep up the post.

RRR

Sorry for the double post. New iPad.

architect said it it looked like overkill

I'm curious about "overkill" in terms of what? Cost? Heat load? Efficiency? You are building an ICF home, so you must be looking at some goals that aren't strictly cost-dependent.

Overkill in terms of retun of long term payback vs.investment for geo. Radiant is must in my book, the dog and I like a warm floor so we are not negotiating on that one. Arctitect sugested a forced air alternative may be less costly give layout.

Yes we are looking at costs closely, not just the construction phase but long term, that is the reason we will build with ICF. We like the idea of the heat pump as a heat sorce, from what I keep reading air source continues to improve, especialy with solar assist as a way to help reduce operating costs.

RRR

glad you like the info. I have about a week's worth of data to pull out, I'll do that in the next couple of days and post an update.

Radiant floors in tight houses are not always warm. "Not cold" might be more accurate - depending on the house, of course.

Jeff

Posted By jbaron on 21 Feb 2011 01:42 PM
Radiant floors in tight houses are not always warm. "Not cold" might be more accurate - depending on the house, of course.

Jeff

Or maybe "depending on the heat load per unit of heated floor area", which will vary by both house and climate.  In very high-R houses the heat loads won't necessarily be high for the floor to be significantly above room temp while meeting that demand for heat, but it'll be warmer than the ceilings or walls. 

In conventionally-framed 2x4 or 2x6 buildings with R10-R15 whole-wall R-values they'll be pretty warm when it's in the 20s or lower F outside.  In homes with R30+ whole-wall R it might have to -5F outside before that cushy cruisin' in yer socks appeal shows up, but at least it'll always be comfortable in bare feet, if not noticeably warm to the touch.

you know, in our shop I'm noticing that floor temps of 72-73 degrees (wood surface) are VERY comfortable. not chilly or even cool. Just comfortable.

Certainly different than 67 degrees (natural floor temp in here when not heating).