please explain staged heating on heat pumps

andrelaplume2February 25, 2009

Just bought a trane 3T units w/vs air handler and 15KW plates.

What is staged heating? One guy says it involves an outside stat that governs when the 1st stage (5KW) kicks in....say at above 35 degrees. Perhaps below 35 degrees the entire 15KW kicks in. Upside, you do not ALWAYS run at 15KW when aux heat is required. Down side, he says sometimes you want to quickly warm your home and if its a little warmer out that day, only the 5KW kicks in and it will take longer to warm the house.

Other guy says it happens automatically but did not mention an outside stat or how it works.

How does this work? Is it worth having or can it be a nuisance? Does it cost more to install? In reality how much does it save over a straight 15kw, whichI would think would kick in for a shorter period of time and warm up faster?

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I will try to answer your question.

heat strip backup is usually sized for the emergency heat needs of your home in case of a mechanical breakdown of your outside HP condenser. for example, if your home requires 30 KBTUs at design temperatures, then you would probably require 10 KW heat strip. But if your HP condenser is operating correctly and still putting out heating BTUs, then you really would not require the activation of the full 10 KW strip. It would be better to have two 5KW strips where only the second would be required on those extra cold days. Any Trane installer worth his salt should know how to wire the backup strips as staged. Operationally, it will save you at the meter. Why use the full amount if you don't need it?

for your situation, I would suggest two 7.5KWs or perhaps a 10 and 5 KW. one 15 KW heat strip puts out about 51 KBTUs

BTW, what did you end up purchasing?

Good Luck

    Bookmark   February 25, 2009 at 1:43PM
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Well, I got the trane 3T ton (not sure the number) paired with the stimulous qualified '40' variable speed air handler. $6800 out the door. I could have gone with another company a little cheaper but this one appeared more thourough and I believe did a more accurate load calc. The guy still feels a 2.5T would be adaquate but he did a load calc or something for my basement as said if I had any intention of adding numerous ducts and a return down there at some point, then I should opt the 3T.

He said it included 15KW. He did not get technical on them. In fact he was the one who mentioned how, years ago these things worked in conjucntion with an outside stat. From what you say its all in the way the installer hooks it I am not clear here on what I am getting regarding the strips...the paperwork went out today, I should get it by weeks end, I can post more info then. I could get it installed next week if I wanted...wouldn't you know they say a snow storm is coming!

I think I made the right decision, I'll just need to understand how this aux heat thing works and insure they hook it up right...perhaps its a given that they hook it up the way you say.

If I remember you reccomended a Honeywell stat right. I'll live with the non programmable one the system comes with for a while but then I want to upgrade that.

Thanks for al your help.

    Bookmark   February 25, 2009 at 2:15PM
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Staging the strips can save a bunch of money in just one winter especially if the heat pump isn't shut off when it is so cold it can't even come close to keeping the temp satisfied. Here is a good example and good reason to use the vision pro stat with outdoor temp sensor or some other low temp cutout for the heat pump.

Here are some numbers for our system.

Heat pump draws 20amps

Heat strips draw 50 amps per stage with 2 stages.

Total heating available is 120amps.. but the air handler should be able to heat the home with strips only so there is not cost effective to ever run all three.

Temps in the 30's-40's.. heat pump works with no need for strips... 20amps consumed plus blower motor!

Temps down in the 20's the heat pump can't quite keep up and needs some help satisfying the tstat at times with no staging on strips. 120amps plus blower motor UGH!

Same scenerio strips are staged... Tstat calls for 1st stage of strips with heat pump 70amps plus blower motor big difference.

OK now its dropping to a bone chilling 0 at night and 18 during the day and the heat pump is set to cut out below 15 degrees on the Honeywell Vision Pro and the unit is staged. Above 15 degrees the heat pump runs and cycles one set of strips to keep the stat satisfied. Without any need for the owner to change or forget to change the stat to emergency the stat shuts the heat pump off at 15 degrees and relies solely on the staged strips until the next morning or until the temps comes back up. There is no need to worry about forgetting to set the stat on emergency or setting it back into normal mode. Amps used above 15 degrees 20-70... Amps used below 15 would be 50 alternating to 100 when the second stage comes on.

Staging and temp lockout can both save quite a bit of money and wear and tear on the outside unit if it gets miserably cold out.

    Bookmark   February 27, 2009 at 12:02AM
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Some good stuff here, I think, didn't run all the numbers.

I assume the 20 amp HP example was not for the 3 ton unit. 20 amps at 240 volts is almost 5KW (VA)... that would be a very inefficient HP, in my experience. My 4T (COP 3.5) uses only 3.3KW (VA) and that includes the blower and all pumps.

My first stage of resistive auxiliary heat is 5KW, not 15KW and my second stage auxiliary is an additional 5KW or a total of 10KW. Never need that, even at zero degrees outside.

    Bookmark   February 27, 2009 at 5:52PM
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The numbers I tossed out were just for an example. I installed the Honeywell stat with outdoor sensor and set up the staging on my builders grade HP with a horribly set up duct system and it more than paid for everything the first heating month which was colder than the previous month.

    Bookmark   February 27, 2009 at 8:11PM
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I've got a 4 ton Climatemaster Tranquility 27 GSHP 2 stage with 15 kW aux heat. I don't know how it is staged or what the Honeywell VisionPro IAQ stat is set to kick in for 1st and 2nd stage. I have to set the stat to Heat in fall and Coll in spring b/c no Auto setting even though the manual says there's one. We leave the breaker for the Aux Heat turned off til Tgiving every year (2nd winter in house) since the T27 seems to keep up with demand OK til then. But boy, does our bill spike in Jan and Feb! We go from avg 40 kwh/day in cooling season to 48 kwh/day in Nov, 58 in Dec, and then mid-high 70's in Jan/Feb. Feb 08 was 74 kwh/day, Feb 09 was 77 kwh/day!

Installer says don't program the stat (we drop it 1 degree upstairs at 10pm, go up 1 degree to 68 at 6am, down to 67 at 8am, up to 68 at 6pm. Downstairs we drop to 65 at 10pm, up to 66 at 5:30am, 67 at 6:15, 68 at 7am). He says recovery (even though IAQ is running) will cause 2nd stage to kick in and cost more than if we kept it constant temp. Should I ask how strips are wired and what kick-in temp for aux heat is? Our stat never displays when Aux Heat is on - only see "Heat on" and sometimes "Recovery" displayed under set temp.

Are we just keeping our house too warm (can be 60 degree difference in inside/outside air in Feb)?

    Bookmark   March 13, 2009 at 9:42PM
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