Daikin Altherma COP Calcs
Last Post 14 Mar 2011 11:51 AM by ICFHybrid. 45 Replies.
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BadgerBoilerMNUser is Offline
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21 Feb 2011 09:04 PM
If you have windows you will have "cold" floors, as Rob suggests in the mid to low 60's. With ERV or HRV the load will increase. Comfort is the absence of discomfort not necessarily a floor that is noticabley warm to the touch. More like a warm handshake unless under design conditions as Dana astutely points out.
MA
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22 Feb 2011 09:40 PM
Thanks for all the info.

Dana1... With last night down to -15, it sounds like it may be the right choice I may get my warm floor one in a while. Rob I will take not cold to the touch, just don't want to have carpets. MA ... I will take an absence of discomfort given the past few nights.

Any thoughts on the solar assist option of the Daikin Altherma, does it have payback.

RRR
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23 Feb 2011 03:01 PM
Unless you had R60 walls and extremely minimalist glazed area you'd be feelin' the love in your toes on a radiant floor at -15F outdoor temps. (And you would be guaranteed the absence of discomfort at mere 0F or +15F outdoor temps.) The Altherma won't run at high efficiency with -15F air though, and total output might not be sufficient unless you've gone to a high-R ICF (the true steady-state R, not some mass-factor "equivalent-R".) Make sure that the design-condition heat load is within the specs of the the unit at the outdoor design temp unless you have an auxilliary heating plan to make up the difference. (The mass of ICF construction will buy you something on peak heat loads, but not 20%, and the output/effeciency of air source heat pumps fall pretty dramatically at sub-0F.)

Payback on solar thermal can be very long under the best of circumstances- but with a high-efficiency heat pump even less so, unless heavily subsidized. You'd have to do the math on your actual location loads & available subsidy to make that assessment. Unless your ICF already has 10" of EPS and you've insulated the basement slab to R16+ you might get better "payback" out of putting the same money into boosting the R value of the building than adding any type of active solar. The amount of solar that it would take to make a difference on space heating is still quite a bit even with R30 walls. The payback on sufficient solar for a significant boost in domestic hot water heating efficiency would be a lot less, but still hard to rationalize at the high summertime and shoulder season COPs you'd get out of the Altherma.

Designing the building site-specific to optimize passive solar is a very good deal in high-mass houses though- easier to get the benefit than with lower mass construction.
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23 Feb 2011 03:09 PM
It falls below zero, but it doesn't fall as fast as you might think. you're still at 27kBTU/hr on the big unit's HEAT PUMP (not backup) at -4deg F. 6kw more on the backup. below minus 4 it appears to continue falling more or less in line with the performance indicated by the MFG data, according to the MFG, I have not yet logged temps below -4 deg F.

an area with -15 design temps still wont see that very often. We ARE a -4 design here, and we only saw that temp twice this winter. the number of hours as you approach design gets pretty small. Still, you probably want to be warm.

I have not priced out the solar add on, not sure if it makes any sense. typically I say solar heat doesn't make much sense. Solar DHW can.
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ICFHybridUser is Offline
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23 Feb 2011 03:27 PM
Or maybe "depending on the heat load per unit of heated floor area", which will vary by both house and climate.
Couldn't one "concentrate" the tubing a bit in order to get warmer floors where you walk? In the kitchen, for example, why put tube under places that you know will have cabinetry above? Why not reduce the overall area and put the tube where you walk so you will have a warmer (toe-friendly) surface?
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23 Feb 2011 03:29 PM
possible, but the price is higher operating water temp.
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23 Feb 2011 03:30 PM
If you have windows you will have "cold" floors, as Rob suggests in the mid to low 60's.
Wouldn't that be just the opposite? Don't windows increase the heat load and require an increase in the heat output needed per unit area of floor?
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23 Feb 2011 04:34 PM
possible, but the price is higher operating water temp.
I'm sorry, but I'm not following that one, either. Wouldn't "concentrating" the tubing (i.e. reducing the spacing) raise the temperature of the surface without requiring an increase in the supply temp?
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23 Feb 2011 04:42 PM
no, you are reducing the square footage of your emitter, or this wouldn't work.

reducing the square footage of the emitter means you need more heat per square foot emitter

that means you need a higher water temp. You might offset that slightly with a tighter tubing on center, but you won't eliminate it. depending on your situation though it may, or may not be a big deal.

and obviously with some install methods this would be impossible or a PITA.
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23 Feb 2011 04:59 PM
reducing the square footage of the emitter means you need more heat per square foot emitter
Sure, assuming all other things are equal, but when you reduce the spacing, you get more heat per square foot emitter right there.
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23 Feb 2011 05:01 PM
as I said, that will offset the gain but will not eliminate it.

6" o.c. pipe, for example, does not have twice the output per square foot of 12" o.c.
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Dana1User is Online
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23 Feb 2011 06:15 PM
Somehow I'd mis-remembered it as the heat pump hitting the low 20s on (average, not peak, with defrost cycles counted in) at a bit above 0F. A decently detailed 1600' minimal R16 ICF house would probably still be well under the heat pump + backup limits built into the Daikin at -15F.

Seasons will vary- our 99th percentile design temp is 0F, and we've seen -4F almost as many times as you have this season. (I think -9F was the low for us so far this year.) I've seen it as low as -18F here back in the mid-'90s- a sizable fraction over the design heat load, but aside from a few frozen pipes, not much of a "problem" since typical heating systems I've seen in this town have outputs of ~200-500% of actual design day heat load... ;-)

Active solar rarely makes sense here in the NE, but passive solar tempering usually does. Even in sunny places with high diurnal temperature swings like modert or high altitude NM/AZ/UT the economics of active solar aren't usually there for new construction where you get more R/$ than in retrofit situations, and passive design performance in high-thermal mass houses gets to be pretty good. As retrofit in those places active solar with natural gas backup can sometimes beat geo- depends on the particulars. (Chainsaw-retrofit upgrades of the building envelope haven't really caught on, but that might be equivalent or better investment than massive solar for a low-thermal performance building.)
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23 Feb 2011 08:03 PM
6" o.c. pipe, for example, does not have twice the output per square foot of 12" o.c.
Oh. I think I see what the speed bump is. I'm not making any assumptions like that.

One would have to redesign the layout but it sounds like it is possible to concentrate the tubing and get a warmer floor where it counts.

I'm not sure I want heat under food storage areas anyway.

Or under the refrigerators.
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24 Feb 2011 09:40 AM
good design already skips those areas, typically, or at least doesn't consider them "active heating floor".

to do layout design like you want, you would have to know what your per square foot load is, adjust it for the floor you don't want to pipe, and find your new coverage/spacing target for the areas you do want to cover.

to go from neutral to warm floors though, you will raise your water temperature target at least a little, and you will have uncovered floor area in the normal "walking space". You have prioritize traffic, standing, or sitting areas to successfully do what you're talking about and skip other areas.
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01 Mar 2011 11:44 PM
Rob, an excellent post.

Are the Daikin Altherma units actually available in Canada and the USA?

If not what ASHP/Hydronic units are?

Thanks in advance

John
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02 Mar 2011 08:39 AM
I know the Unichiller has been around awhile, and aermec has made some posts. Daikin althermas are available in the US and Canada though, definitely. There are some areas still where it's hard to find a trained installer I'm sure.
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02 Mar 2011 10:33 PM
Maybe i missed something but can you post the exact model number and size?

(also, just to double check this is a air-to-water/hydronic heat pump correct?)

Thanks

John
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03 Mar 2011 09:18 AM
we're using the 054 split system, on a 30kBTU design heat load (so it's "oversized). it is an air to water hydronic heat pump. We bumped up our water temperature to 113 Deg F two days ago, and just got some nice cold weather (yay!) and so we will have an update soon for operation at that temperature under a good range of conditions as well.
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03 Mar 2011 09:28 AM
Posted By NRT.Rob on 23 Feb 2011 03:09 PM
I have not priced out the solar add on, not sure if it makes any sense. typically I say solar heat doesn't make much sense. Solar DHW can.

Rob,

I thought the solar option for the Altherma was for DHW only?  My understanding of the Altherma solar add-on was an exchanger attached to the DHW.

For DHW, I'll argue that it makes sense because it lifts a load off the 6kW backup when you're approaching the maximum output of the Altherma.

Victor
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A 4350sqft cold climate Net Zero Energy initiative
NRT.RobUser is Offline
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03 Mar 2011 09:31 AM
Maybe I should have said "I haven't even looked at the solar option"

I have no idea what it does. if I use a daikin for DHW though, i plan to maintain a lower temp (like 100 degrees) and simply boost up with an external on demand sized for my actual needs.
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