Heat Pump Air Temp from Register

SCBIRDDecember 2, 2011

I had a new heatpump put in a year ago and last winter I was pleasantly surprised at how warm the air seemed to be coming out of the registers, however this year it seems to feel a lot cooler. This morning it was 29 degrees outside and the thermostat was set to 67 degrees. The air coming out of the register closest to the air handler (which is under the house) was averaging around 87 degrees. After about 15 to 20 minutes of run time it did go up to 89 degrees and raised the temp to the desired setting. I checked it a few mornings ago when the outdoor temp was 35 and I had 89 degrees at that time too with no aux heat either time. Does this sound about right for these temps or do you think I should be getting a few degrees warmer? It's a 1500 seer unit if that makes any difference.

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tigerdunes

Sounds about right as long as that supply temp was without heat strip auxiliary.

Supply temp along with BTU output drops as outdoor temps dip below freezing.

IMO

    Bookmark   December 2, 2011 at 10:35AM
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brickeyee

As the outside temperature falls the ability to extract heat declines.

When you get near 32 F outside frost can start to form on the exterior unit (now an evaporator) and further decrease output, and require energy to remove during a 'defrost' cycle.

To limit cooling of the house heater strips are often turned on and the heat pump placed back in AC mode to heat the exterior coils (now again acting as a condenser) to defrost them.

    Bookmark   December 2, 2011 at 10:49AM
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tigerdunes

Brickeye is correct about the defrost function.

I am surprised that so many HP manufacturers still rely on inefficient time/temp method of defrost as opposed to the superior electronic demand defrost that eliminates unnecessary, nuisance, and epensive defrost calls.

IMO

    Bookmark   December 2, 2011 at 10:54AM
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SCBIRD

Frost did build up this morning on the outdoor unit and the temps coming out of the register dropped as the frost built, but the unit did go into defrost and sent low 70's air out of the register while in defrost. The auxiliary heat never did come on (but I have verified that the aux is working). A few minutes after the unit defrosted was when I saw the output temp peak at 89 with not aux heat.

So all of you think with an outdoor temp of 29 and 67 set on the thermostat that 89 degree output at the register is sufficient and I don't have a problem?

I don't want the expense of a service call if the unit is working properly. Thanks!!!

    Bookmark   December 2, 2011 at 11:11AM
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tigerdunes

HP should not go into defrost without auxiliary unless you have some type of lockout on your system.

IMO

    Bookmark   December 2, 2011 at 11:14AM
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SCBIRD

I am feeling a little better about it now. It's up to 55 degrees outside and I bumped the thermostat up 2 degrees to 69 and let the unit run for about 15 minutes and then checked the air coming out of the register and it's 98 degrees. Provided it was 29 degrees this morning and the supply heat was only 10 degrees less than at 55 degrees, that doesn't sound that bad now.

    Bookmark   December 2, 2011 at 1:26PM
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dadoes

If your indoor temp is 67F-ish and output is 70F during defrost, then your auxiliary must be running or the output temp would likely be 57F or less -- the system switches to cooling mode (air conditioning) during defrost.

    Bookmark   December 2, 2011 at 1:29PM
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SCBIRD

Thanks for the replies. I never did see the aux light come on, but it's possible the auxiliary may have kicked in during the defrost when I wasn't watching it. My main concern was the supply temp only being 89F without the auxiliary heat running when the outside temp was 29F. I was thinking it should have been in the mid 90's at that point, however after seeing it get up to the upper 90's at 55 degrees, I think the unit is probably working correctly. Agreed?

    Bookmark   December 2, 2011 at 1:49PM
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weedmeister

Chances are the light will not come on during defrost. I don't think mine does either.

Your unit is fine. Sounds like it's putting out better heat than my SEER14 unit.

    Bookmark   December 2, 2011 at 3:42PM
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brickeyee

"as opposed to the superior electronic demand defrost that eliminates unnecessary, nuisance, and epensive defrost calls. "

$$$$$
Demand defrost reacquires extra parts and costs money.

    Bookmark   December 3, 2011 at 12:51PM
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tigerdunes

for brickeye

not meaning to be argumentative but I stand by my statement and disagree with yours.

I am surprised that so many HP manufacturers still rely on inefficient time/temp method of defrost as opposed to the superior electronic demand defrost that eliminates unnecessary, nuisance, and epensive
defrost calls.

time/temp defrost method is used because it is so cheap.Kind of like hand crank windows versus power windows. Demand defrost saves money. Now if one lives in a mild winter heating climate, then not as big of a deal.
I live in SE and would not recommend a new HP system without
explaining the benefits of demand defrost. Most homeowners require education on this feature and difference.

IMO

    Bookmark   December 3, 2011 at 1:16PM
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countryboymo

My demand defrost probably paid for its 'extra cost' in energy savings the first year. My 'old' unit which was a 2yr old builders grade went in defrost on the timed rate and stayed on for the full 10 minutes before going back into heat mode. The new system rarely goes into defrost in comparison to the old one even at 20 degrees. It will go into defrost more often than a timed system if it is below freezing and snowing or in a freezing rain event like it is designed to. My old system would be a block of ice because the 'timer' was not ready for defrost yet.

If the heat strips are staged in different increments say 10kw and 5kw on 15kw strip in some instances you can put the defrost on the higher stage or strips to do a better job of tempering the air. I had an issue with 70 degree air in defrost mode when defrost only activated the 5kw leg of strips. I switched it to the 10kw leg and now have close to the same air temp as when the pump is running normal.

    Bookmark   December 3, 2011 at 2:00PM
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tigerdunes

Yep

Countryboy is right on target...

    Bookmark   December 3, 2011 at 2:15PM
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ionized_gw

Demand defrost refrigerators, by my understanding, have been available for several years.

    Bookmark   December 5, 2011 at 3:30PM
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brickeyee

Demand defrost requires extra parts and costs money.

You think it comes without any other parts?

Many folks shop just on price.

Notice I had no argument about it being 'better.'

Just that it requires more parts and costs more.

Unless you know someone supplying it for free.

    Bookmark   December 6, 2011 at 9:33AM
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countryboymo

Demand defrost is an 'option' that will add to the cost on a 13 seer. On a 15 seer unit DD is usually 'standard' equipment. The initial cost is higher of course than timed defrost but the extra cost is quickly offset in savings.

Of 'extra's' that are available on a system.... if its below freezing very much demand defrost has one of the quickest paybacks.... if its more hot and humid then a txv.... if its like here where you get the heat and humidity along with a long spell of well below freezing than a 15 seer with both options standard is the minimum "baseline" I would recommend.
I was blown away at the difference and rarity that my DD system actually goes into defrost mode in comparison to my timed system. Every minute a system is running in defrost that does not have to be is burning a tremendous amount of load that is not needed only to warm the outside with strips.

I had 20kw of unstaged strips and 13 seer 3.5 ton timed defrost and was borderline on a 200 amp service. When I finish my basement I was going to have to upgrade to a 400 amp service. I sealed the ductwork, had the heat pump upgraded to a 15 seer 3 ton with 15kw of staged heat strips with a good outdoor sensing stat. I dropped the total load enough to be able to finish the basement easily without needing to drop the $$ on a 400 amp service and also reduced my electric bill considerably. I also did some home sealing but still need to get in the attic and do more.

OH and the house is more comfortable and the noise is much less. Sorry to go off on a tangent but it just amazes me that upgrading my heat pump and doing a few other things allowed me to keep from spending thousands to upgrade my service... only to have a higher bill to pay for the increase in load.

    Bookmark   December 8, 2011 at 12:35AM
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thull

"Demand defrost requires extra parts and costs money."

A timer is a part that costs money, right? So, you're essentially replacing that with a small board with a thermocouple that clamps to the coil. I replaced the defrost board on my Rheem, and I think it cost $80 to $100. I'm sure the OEM cost is much, much lower.

Whether there are licensing/patent issues for the concept is a different issue. That likely makes it more expensive to implement than just the parts.

Anyway, the extra cost likely pays for itself in a season of use.

    Bookmark   December 10, 2011 at 12:19PM
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brickeyee

"A timer is a part that costs money, right? So, you're essentially replacing that with a small board with a thermocouple that clamps to the coil. "

The timer is Alfred there, the design cots are sunk (and probably recovered).

It takes a lot more tan just a thermocouple. All those parts on the small board cost money to design and ten build).

The cost may be recovered quickly by the user, but is\t is an additional cost.

Why do you think the government forces higher deficiency equipment?

Consumers will not spend the money even if the savings are worthwhile but there have been plenty of schema sold that will never pay back their cost before failure or replacement.

The government standards are base solely on energy efficiency, NOT total cost of operation.
More complicated systems have more failures offsetting any savings in energy costs.

Many of the early ground source systems turned into expensive disasters for the consumers.
Buried systems need VERY good corrosion protection for long life.
Even if they are in a 'dry hole' it IS going to fill with water from the surface over the long term.

    Bookmark   December 10, 2011 at 3:06PM
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