Heat Strips.. to stage or not to stage, that is the question.

[Robinson2]

Hello all… first let me say thanks for all the great advice everyone has provided in this forum. It has already been a great help to me as I decide on a new system.

I am trying to understand the pros and cons of a staged heat strip. Can someone explain to me in layman terms how to decide when given a choice of a standard heat strip with one power level, or a system with heat strip(s) that have two or three levels.

Planned heat pump is 2.5 ton single stage compressor with matching air handler with “staged” ECM blower. Thermostat is either a Honeywell 9000 or Trane XL 950. Climate is Charlotte NC.

Also one of the HP models I am being quoted on is listed in the AHRI product directory as discontinued. Is this a concern?

Lastly one of the quotes involves replacing the copper lines to and from Heat Pump to air handler.. is this a good idea on a 20 year old home if they otherwise appear to be OK? (I should mention that the reason for replacement is the Freon is low, and its 20 years old)

[dan sw fl]

Heat strips are used for both auxiliary (supplemental) and emergency heating and must always be staged when used with a heat pump.

Google auxiliary heat strips for more discussions / FAQs.

[Robinson2]

If your saying that the heat strip is always staged in that it is always OFF (in normal heat pump mode, let’s call it stage 1) or it is ON (in supplemental, defrost, emergency mode, let’s call that stage 2) then I understand.

However what I am asking about is Aux heat that comes on at different power levels during normal heat pump mode (at least) depending on the need. For example if the heat pump just needs a little help to maintain temp, the strip might run at 4 kW for example, then if needed switch to 8 kW.

None of the quotes I original received suggested such an arrangement although they said it could be done when I inquired. (One said they could put a heat strip or strips that run at three different power levels). The question of SHOULD it be done is not being answered to my satisfaction.

By the way I did a lot of “Googling” before I came here for information, but mostly used the term heat strip and not auxiliary heat. The most helpful page I saw was this:
http://ths.gardenweb.com/forums/load...300189890.html

Using the terms you suggested I still don’t seem to find good answers so if you have specific web sites to suggest that would help.

Heat strips are used for both auxiliary (supplemental) and emergency heating and must always be staged when used with a heat pump.

Google auxiliary heat strips for more discussions / FAQs.

[mechanical'al]

do you have gas aval.

[Robinson2]

No, Elect only.

[mechanical'al]

Propane? why couldn't you get propane?

[Robinson2]

Propane? why couldn't you get propane?

Well of course I could get propane.. big tank in the yard, truck delivery, etc.. what I meant was there is no gas service to the house. Nor is there any in the area.
Charlotte is pretty mild climate and my experience has been that a heat pump system does a pretty good job overall so I have never felt it was worth the trouble to get propane.

[isuredo]

Heat strips should be sized to provide all the heat needed in case the heat pump is broke down, all multiple strip heaters are staged, one reason being to not have a huge power draw all at once on your panal, the t staT knows when the heat pump isnt keeping up and will send a signal for aux heat, which in turn thru a bank of relays (sequencers) brings on the strips one by one, as far as i know only a carrier communicating system is capable of only using whats neccesary, anyone please correct me if other manufacturers are doiing this also

[ga-hvac-tech]

Good question, lets see if I can shed some light on this subject:

First: Yes, Charlotte is a mild climate, so a HP with back-up elec heat probably would be fine. Some folks are comfortable with HP/Elec in really COLD climates, personally I would not be.

A HP generally can handle the heat load down to somewhere in the 30's D range... depending on a lot of variables. Inverter drive mini-splits perform better, some can provide enough heat down to 0 (zero) outside... however these are generally not ducted systems.

When the HP looses its ability to heat (without elec backup), the air coming out of the vents is first warm, then temped, then cool, then uncomfortably cold... however the HP is still producing heat and doing so for less energy per BTU than elec strips. There is a point where the HP is no longer helping, and it should cycle off. When the HP is just below its ability to heat alone, a small amount of strip heat is needed... yet when it is seriously cold outside the full amount of strip heat is needed.

If it were me, and I was using a premium thermostat like the HoneyWell 9000 series (IMO one of the better stats available), I would definitely ask the contractor to stage the heat strips. The HW 9000 series is capable of 4H and 2C, so one could do the following:
H1 = Single stage HP
H2 = first strip
H3 = second strip
(if available)
H4 = third strip
or if using a 2 stage HP
H1 = low HP
H2 = high HP
H3 = low strip
H4 = high strips
In each scenario above, each successive stage of strips means adding another strip while the previous one(s) are operating.

The HW9000 has the ability to 'stage' all this... not all premium stats do.

Let us know what you decide, and how it works out.

[EMETH]

My professional and personal experience has been to go with one heat strip.

Now we come to the discussion on the proper way to operate a heat pump. NEVER TURN IT OFF!!!

If you turn your heat pump off or setback too much, depending on the outdoor ambient, you will use more energy and it will take longer to reheat your house before you arise. You could have an outdoor t'stat installed and set to the balance point to limit the strip.

I would never advise anyone to setback their heat more than 4 degrees max nor setup their cooling. In my experience it takes more energy to recover than it does to maintain. This, of course, assumes your comfort settings are not 70 for cooling and 78 for heating (that brings a whole new level to your electric bill).

Programmable stats are good in regards to anticipating and resetting to occupied temperatures; they can provide some moderation in energy consumption by delaying or preventing aux strips according to calculated recovery curves.

In my own last three homes, I wired the heat strips to "E" rather than "Aux" or "W2"; I never setback more than 4 degrees and it is only when the unit defrosts that I can smell the strips come on (actually, in 1 house I never did install any strips and was always comfortable; sometimes the unit would defrost in the middle of the night, blow cold air for a few minutes and go right back to heating normally).

I prefer the Honeywell VisionPro 8000

My own professional and personal experience and my own . There is no obligation to attempt to replicate my results.

Let the flaming commence.

[ga-hvac-tech]

Just my ; different climates. I grew up in Houston TX, where one can generally count the freezes on their hands (sometimes one hand or no freezes one winter)... now I live in Atlanta where one counts the nights in the teens on their hands.

There IS a point where a HP is just running... then there is the comfort issue.

Since the person looking for advise suggested they were going to use a HW 9000, why not take advantage of the features. I know Charlotte can have a humid summer, using an ECM driven AH would help with humidity control... the HW 9000 will handle dehum and keep the home comfortable year round.

[dan sw fl]

If your saying that the heat strip is always staged in that it is always OFF (in normal heat pump mode, let’s call it stage 1) or it is ON (in supplemental, defrost, emergency mode, let’s call that stage 2) then I understand.

However what I am asking about is Aux heat that comes on at different power levels during normal heat pump mode (at least) depending on the need. For example if the heat pump just needs a little help to maintain temp, the strip might run at 4 kW for example, then if needed switch to 8 kW.

None of the quotes I original received suggested such an arrangement although they said it could be done when I inquired. (One said they could put a heat strip or strips that run at three different power levels). The question of SHOULD it be done is not being answered to my satisfaction.

By the way I did a lot of “Googling” before I came here for information, but mostly used the term heat strip and not auxiliary heat. The most helpful page I saw was this:
http://ths.gardenweb.com/forums/load...300189890.html

Using the terms you suggested I still don’t seem to find good answers so if you have specific web sites to suggest that would help.

FROM TIGERDUNES who IS ALWAYS providing proper guidance :

"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.
________________________________________ - - _______________________________________
When 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?"

An explanation probably doesn't get any better than that.
---------------------------------------------------------------
Auxiliary Heat comes on when the heat pump can not keep the house at the thermostat setpoint.
Auxiliary Heat should be ON at less than the balance point which normally falls in the 24'F - 35'F range.

Emergency heat strip (ALL strips) is used when the heat pump is not working.

[BaldLoonie]

While most mfrs. wire their electric furnace so you can stage the strips, few thermostats have that capability and for cost reasons, nobody uses outdoor stats anymore. In the old days, and I saw one we took out recently of that vintage, they put an outdoor stat in so the full strip heat doesn't come in unless it's below a certain outdoor temp. Now, Most stats don't have the capability of anything more than on & off. The Prestige GA is showing can have 2 stages of compressor and 2 stages of backup. The Vision Pro IAQ can stage the backup as well. Some have and E and AUX terminals but most won't stage. They bring on E when set in EM position. AUX comes on as a 2nd stage.

But back to the OP, the VP IAQ or Prestige IAQ can stage the backup. I would guess the 950 would as well. The key is making the installer do it

[garyed]

You're going to get different answers from different contractors because this is not a black & white question. I'm not a big fan of staging heat strips unless you've got strips that are grossly over sized compared to the pump. With a 2.5 ton heat pump I wouldn't consider staging them unless I had at least 15kw or more to stage. You also need a thermostat capable of 3 stage heat to do it. Some of the original heat pumps used to use an emergency heat relay to kick in extra stages of heat strips for emergency heat but the manufacturers decided it was really not necessary. Besides the same thing can be achieved with a t-stat that has an emergency heat terminal. I've heard the arguments about the compressor running more with less auxiliary heat & saving money but I'm not convinced staging the strips saves any noticeable energy at all.

[Robinson2]

Thanks to everyone for your comments… I have a much better understanding now even if I am undecided if I should request staged heat strips or not. It sounds like staging the heat strips might save me some in operating cost, or it might not, and that it is a little more complicated to set up a system with heat strips running at different power levels. So my plan is to not discuss this with the sales person any further and let them put in whatever strip they think is best and that they are comfortable dealing with. I don’t know how you guys find free time to answer questions like mine but I am glad that you do. Thanks again.