John7
Basic Member
Posts:114
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| 17 Jun 2011 02:58 AM |
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Does someone have some temperature performance type charts for Altherma units?
The brochure I have says something like "supply temperature to 125*F", but in the notes says "with 6kW heater".
I need to know what the heating capacity is at 18*F, and what the rise in return to supply temperature is.
Also at what point the electric heater kicks in.
Thanks
John |
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NRT.Rob
Veteran Member
Posts:1741
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| 17 Jun 2011 09:49 AM |
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yes. send me an email and I can send you the output tables.
Basically the heat pump will contribute to some max water temp, related to outdoor temp.
electric backup is added to this. if you need higher water temps at a given outdoor, the split between the two depends on the return temp. basically the heat pump will provide water temps up to the maximum rated at a given outdoor, so if return water is lower than that, the heat pump will contribute up to that amount and the electric booster will do the rest. |
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John7
Basic Member
Posts:114
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| 18 Jun 2011 01:20 AM |
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Posted By NRT.Rob on 17 Jun 2011 09:49 AM
yes. send me an email and I can send you the output tables. Basically the heat pump will contribute to some max water temp, related to outdoor temp. electric backup is added to this. if you need higher water temps at a given outdoor, the split between the two depends on the return temp. basically the heat pump will provide water temps up to the maximum rated at a given outdoor, so if return water is lower than that, the heat pump will contribute up to that amount and the electric booster will do the rest. Thanks Rob. I realize the return temp and outdoor temp are key in determining the heat pump only supply temp. I assume the flow rate and actual BTU capacity of the heat pump also affect the supply temp. Anyway how do I email you? John |
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NRT.Rob
Veteran Member
Posts:1741
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| 18 Jun 2011 09:20 AM |
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rob@ my website
I'd post it but I can't see to get it into a format that works for this bulletin board, either too big or disallowed type. |
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John7
Basic Member
Posts:114
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| 19 Jun 2011 02:04 AM |
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Rob
I just emailed you my info.
Just a quick question about the Altherma, is a supply temp of 120*F reasonable? (I realize the return temp and outdoor temp also factor in). The reason why I ask is i am going to ask my designer to reduce the bathroom supply temp to that of the living room (120*F) and in that way 120*F is the max for the entire house (not 127*F).
Thanks
John |
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ICFHybrid
Veteran Member
Posts:3039
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| 19 Jun 2011 10:57 AM |
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Here is the link to the page on which exists the Daikin Altherma Engineering Manual, if that helps.
http://www.daikinac.com/commercial/docsEngineering.asp?sec=docs&page=58
It's the document titled 'Daikin Altherma Split Type and Monobloc Type Engineering Data'
It's now a 37 MB .pdf with about 150 pages. |
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John7
Basic Member
Posts:114
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| 19 Jun 2011 12:21 PM |
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Thanks IFCHybrid
The table on page 83 is a bit alarming. If I am reading it correctly the heat output for 122*F water at 19*F ambient is ZERO. The cell is blank.
I also note the COPs drop significantly with higher water temperatures. So that makes me ask a basic question about the system. If I have a couple of rooms designed for 120*F water, does that mean only during the three coldest days of the year and with lower temperature water on most other milder days? Or does the system always run those rooms at 120*F but modulate the flow (on/off, on/off)?
Thanks
John |
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ICFHybrid
Veteran Member
Posts:3039
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| 19 Jun 2011 11:51 PM |
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The Daikin Altherma is engineered to be a low-temperature system. That's where it really excels.
Don't forget they have either 3 kW or 6 kW backup heaters for a max of 20kBTU in those cold times.
It has a dual set point, meaning that if you have both low temperature rooms and high temperature rooms and a thermostat from a low-temperature room calls for heat, it only delivers the low temperature, but if a stat from a high-temperature zone calls, it attempts to meet the high temp requirements. In that circumstance, to avoid having all rooms get the high temp, you need to have a mixing system to supply the lower temp rooms. |
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John7
Basic Member
Posts:114
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| 20 Jun 2011 02:31 AM |
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That info makes sense.
I still have a couple fundamental questions.
1) In a typical system does the circulation pump run continuously or intermittently?
2) If my design temp (worst case outdoor ambient) is 19*F, but I am experiencing two weeks of milder weather (say 40*F), does it:
a) decrease the required supply temperature such that my 120*F zone becomes say a 95*F zone, or
b) just circulate 120*F water for shorter periods of time?
If its a) that's great because most of the time the Altherma will be in its "comfort zone".
If its b) and I have a couple of zones designed for 120*F supply does that mean the 6 kW backup will be on everytime the heat pump is on?
Thanks.
John |
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NRT.Rob
Veteran Member
Posts:1741
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| 20 Jun 2011 08:57 AM |
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the altherma has outdoor reset built in. so it would be programmed to run to 120 only at your design condition (19 degrees) unless you are doing something like a fan coil that isn't sized to run any cooler. it would run cooler at warmer outdoor temps.
If you have 120 degree rooms, and a 19 degree design, then you could provide 33kBTU/hr from the heat pump at 122 SWT down to 25 degree outdoor. below that, you are on backup only unless your return temp is below 113 (which is rated for 19 degree outdoor) in which case the heat pump would stay on to help out.
If your heat load is more than the backup element, then, you could be short below 25 deg. F when the heat pump drops out. You could fix that by getting those 120 degree rooms down to 113 degree max... supplemental emitters, perhaps, such as radiator. Or if the heat load is less than your backup capacity, you'll be fine. Or, you'll need a backup heater for that cold weather that CAN meet your load.
Heat pumps are low temp devices. ASHP is even lower than GSHP at this point. this is part of the reason why we push low temp design: it "future proofs" any system to take any heat source, such as high efficiency heat pumps. |
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ICFHybrid
Veteran Member
Posts:3039
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| 20 Jun 2011 09:59 AM |
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Not sure what a "typical" system would be, except to say that the Daikin is like any other in that as long as a thermostat somewhere is calling for heat, the Altherma will be sending (pumping) out water at the temperature you specify in the controls (the setpoint). A dual setpoint system has the ability to send it out at two different temps depending on which thermostat calls for it. It also has outdoor reset which monitors the ambient temperature and automatically boosts the setpoint temp when it is very cold out.
Beyond that, you would need additional system controls, such as the mixing system mentioned earlier or more sophisticated zone controllers, valves and pumps.
If it is warmer outside, the heat pump will have no problem extracting heat from the air and moving it to your heating system, but at some point, when the ambient temperature drops enough, demand will exceed the system capacity to extract the heat and that's when the backup heater coils will come on. |
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dmaceld
Veteran Member
Posts:1465
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| 20 Jun 2011 11:02 PM |
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Posted By John7 on 19 Jun 2011 12:21 PM
The table on page 83 is a bit alarming. If I am reading it correctly the heat output for 122*F water at 19*F ambient is ZERO. The cell is blank.
I also note the COPs drop significantly with higher water temperatures. So that makes me ask a basic question about the system. If I have a couple of rooms designed for 120*F water, does that mean only during the three coldest days of the year and with lower temperature water on most other milder days? Or does the system always run those rooms at 120*F but modulate the flow (on/off, on/off)?
I have a Daikin air to air system so I'm interested in seeing what the Altherma does. Looking at the manual this is what I discern, without spending hours studying it. The blank cells you are referring to means that at those low ambient temps the heat pump will not raise the leaving water temp to the temp for that column. It looks like the maximum rise possible from ambient to LWT is about 94°F, so at an ambient of 19F the max LWT will be about 114F. If you look at the graphs at the beginning of the manual you will see the one labeled Mono-Energetic shows that when the ambient is below LWT set point - 94 the backup heater kicks in to raise the water to LWT set point. I would say the Hydroblock will always output water at the set point. The compressor is a variable speed compressor so if the ambient temp is above, say 50F, and the LWT set point is 120F, and only one part of the system is calling for heat, the compressor will run only as fast as it needs to raise the water to the set point. As far as the COP drop, that's the nature of heat pumps. The closer the source temp is to the output temp the greater the COP. |
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dmaceld
Veteran Member
Posts:1465
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| 20 Jun 2011 11:12 PM |
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Posted By John7 on 18 Jun 2011 01:20 AM
I realize the return temp and outdoor temp are key in determining the heat pump only supply temp. I assume the flow rate and actual BTU capacity of the heat pump also affect the supply temp.
Yes, and no. Daikin heat pumps are variable speed. What this means is the compressor will run only as fast as needed to supply the desired supply temp, up to its max capacity. After the HP has reached max capacity the electric backup adds heat to bring the LWT to set point. The Daikin approach is operate the heat pump at whatever output is required to match the current demand. My air-to-air unit, a VRV-S, basically turns on and off once per day during the heating season. It turns on in the evening when the controller calls for heat, and runs continuously until the next morning when the controller says no more heat. In between the house temp stays uniform within 1°F. |
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dmaceld
Veteran Member
Posts:1465
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| 20 Jun 2011 11:29 PM |
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Posted By John7 on 19 Jun 2011 02:04 AM
Just a quick question about the Altherma, is a supply temp of 120*F reasonable? (I realize the return temp and outdoor temp also factor in). The reason why I ask is i am going to ask my designer to reduce the bathroom supply temp to that of the living room (120*F) and in that way 120*F is the max for the entire house (not 127*F).
From what I read in the Altherma manual I would say yes, but 105°F to 110°F would be better. That way you'll stay in the heat pump capacity range a greater amount of time. From the standpoint of a well insulated home with a low heat load, it may well be quite a bit too high. My house is ICF, 2000 sf, with foam insulation on the underside of the roof deck. I use the crawl space for the supply duct and the attic for the return, with a duct from attic to crawl. I have a 36,000 Btu Daikin VRV-S air-to-air HP with the air handler in the crawl space. The output from the air handler is dumped into the crawl space and comes up into the living space through registers around the perimeter. Our Manual J design temp is 9°F and the coldest this past winter was about -5°F. I have a thermometer hanging in the crawl space. The highest the crawl temp ever got was about 87°F. When I checked the floor temp it was about 84°F. I have doubts that your heating load would ever require your floor to get warm enough to need 120F water. I don't know what you have in your other posts. I'm assuming you're looking at in-floor radiant, right? What kind of construction are you planning on? It will be very energy efficient right? If you are using in-floor radiant you can probably add a lot of PEX tubing at less cost over time and use lower temp water than what it will cost to have a 120F supply temp. |
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dmaceld
Veteran Member
Posts:1465
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| 20 Jun 2011 11:44 PM |
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Posted By NRT.Rob on 20 Jun 2011 08:57 AM
If you have 120 degree rooms, and a 19 degree design, then you could provide 33kBTU/hr from the heat pump at 122 SWT down to 25 degree outdoor. below that, you are on backup only unless your return temp is below 113 (which is rated for 19 degree outdoor) in which case the heat pump would stay on to help out.
If your heat load is more than the backup element, then, you could be short below 25 deg. F when the heat pump drops out. Rob, you sure about that? The spec sheets show the units are rated to run down to 5°F. My VRV-S ran this past winter down to -5°F, even though it also is rated to only 5°F. The Mono-Energetic graph on page 3 shows the HP running all the way down to the lowest rated temp, with the backup heater making up that portion of the heat load the HP can't provide. In the scenario of using an auxiliary boiler, they show the heat pump dropping out at the lowest temps when the boiler carries the entire load. |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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John7
Basic Member
Posts:114
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| 21 Jun 2011 02:29 AM |
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Here are the building envelope spec's (copied from an earlier post):
House design is 1000sq ft basement, 1100sq ft main, and 800sq ft second floor. I am aiming for a "code plus 50%" level of insulation. (For this calculation I am actually comparing the clear-wall values since the anti-thermal bridging benefit of the continuous exterior XPS is lost comparing the code "nominal" R values if you know what I mean.) Insulation to be dense pack cellulose with 2" XPS continuous exterior insulation. Serious air sealing and blower door testing. Although there is not much potential for solar heating in the winter here, roughly half the windows are on the south exposure, whereas north facing windows are limited to just two 24" square units. Windows double glazed, low-e, argon fill (actually nothing special although leakage minimized by installing operable windows only where they are actually needed (fixed glazing otherwise) and those windows are better sealing casements).
Design location: Vancouver, Canada
Load calculation method: CSA (F280) (which I believe is analogous to Manual J).
Outdoor temperature: 19.4*F (although the code says 18*F).
Total area: 3109 sq. ft.
Total Heating Load: 26 210 BTU/hr
I am fairly confident with 26 210 BTU as I took an educated guess at less than 30 000 BTU.
That works out to an average of 8.4 BTU/sq. ft. This seems really moderate.
The one room requiring 120*F supply works out to 16.5 BTU/sq. ft. (room loss / room area).
Questions:
1) Why are my supply temps so high? I have a basement slab, and Joist Trak main & second floors.
2) In view of the outdoor design temperature etc and using a Daikin Altherma Monobloc, what supply temp should I be aiming for? Presumably I can add tubing/loops/wall panel or whatever it takes to get the the top 2 or three rooms down to that number.
Thanks
John
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ICFHybrid
Veteran Member
Posts:3039
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| 21 Jun 2011 08:57 AM |
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1) Why are my supply temps so high? I have a basement slab, and Joist Trak main & second floors.
2) In view of the outdoor design temperature etc and using a Daikin Altherma Monobloc, what supply temp should I be aiming for? Presumably I can add tubing/loops/wall panel or whatever it takes to get the the top 2 or three rooms down to that number. 1) What are your floor coverings? A 120F supply temp works out to floor coverings with an R value of 4 or greater - more like like thick carpet and pads with the Joist Trak. 2) You can see from the Daikin Engineering Data, that for heating efficiency with a heat pump, you want the supply temps as low as possible. That's radiant slab tubing with good conductors like tile or thinner wood floors and underlayments. |
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NRT.Rob
Veteran Member
Posts:1741
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| 21 Jun 2011 09:22 AM |
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16.4 Degrees with joist trak and a wood floor would be about a 110 supply, and you're then in the promised land...
re: dmaceld. at a given outdoor temp, if you read across the output charts, you'll see when the heat pump portion of the unit's output drops out completely. for the 054 heat pump, at 19 degree outdoor the highest outgoing temperature the heat pump can generate without backup is 113 degrees, 29kBTUs/hr. Backup can add up to another 20k or so (6kw) at any water temp up to 131 as long as the flow rates/total btus do not break the backup's capability.
the limits on this unit appear to be programmatic and they are NOT LINEAR. for example: at 25 outdoor, the unit will produce 122 degrees with the heat pump. It will continue to produce 122 degree water until you get to 19 degree, then it drops, all at once, to 113 degrees. It will then stay at 113 until you get to 5 degree outdoor, then it drops to 104 degrees.
IF your return water temp is higher than what the heat pump can produce, then the heat pump is done, kaput, not contributing anymore, and you're on backup only.
It appears that Daikin is not just having the unit work "mechanically" to its abilities. They have electronically managed what it will produce and when, presumably to prevent damage and/or increase efficiency. |
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John7
Basic Member
Posts:114
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| 21 Jun 2011 10:03 AM |
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Posted By ICFHybrid on 21 Jun 2011 08:57 AM
1) Why are my supply temps so high? I have a basement slab, and Joist Trak main & second floors.
2) In view of the outdoor design temperature etc and using a Daikin Altherma Monobloc, what supply temp should I be aiming for? Presumably I can add tubing/loops/wall panel or whatever it takes to get the the top 2 or three rooms down to that number. 1) What are your floor coverings? A 120F supply temp works out to floor coverings with an R value of 4 or greater - more like like thick carpet and pads with the Joist Trak.
2) You can see from the Daikin Engineering Data, that for heating efficiency with a heat pump, you want the supply temps as low as possible. That's radiant slab tubing with good conductors like tile or thinner wood floors and underlayments. My floors consist of 3/4" plywood subflooring and 1/2" engineered wood floor. Kitchen is lino, not eng wood. Mudroom/entrance & bathroom are tile. The designer has used a flooring R value between 1.0 and 1.5. John |
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NRT.Rob
Veteran Member
Posts:1741
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| 21 Jun 2011 10:05 AM |
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should have been 0.5 to 1.0... charts for that app already include a 3/4" subfloor. |
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