View Full Version : Running Heat Pumps in the Summer
07-07-2006, 01:17 PM
I am a home inspector and have not been running heat pumps in the summer months to test for heat. Many of the books and training materials say not to.
Of course this is the same material that suggest that temp splits between 16F-20F are a good indication of cooling system performance. :rolleyes:
This topic came up on an inspector message board and it seems everyone is quoting the same literature, but nobody could point out any manufacturer restrictions. What is being quoted is high pressures possibly causing damage. But again nobody has found anything regarding this in any mfr. literature.
So my question is, is our training material full of it? Can damage occur by running the heat pump in heat mode on say a day when it is 100F outside? Will it really show that the heat pump is working?
My standard recommendation is to get the unit serviced prior to the heating season. In addition to my general recommendation for annual servicing.
Any help/advice would be greatly appreciated.
short of gas
07-07-2006, 01:54 PM
The limitations table in the installation instructions does limit operating a heat pump in high ambient conditions. You run the possibility of the unit going off on high pressure. Most tables show 75 degrees F as the max temp on the outdoor coil in heating
07-07-2006, 02:40 PM
If you want to check the heating in high ambient conditions, I suggest running it for just a minute or so, to see that it does switch to heating. If it works good in cooling all you need to see is if it swithes over to heat. Check to see that the filter is clean. If its not remove it for your heating test. If you do these things, I don't think you will have a problem.
07-07-2006, 06:25 PM
Just a wild idea- couldn't he temporarily cover up maybe 75% of the outside coil so that it gets cold enough to simulate acceptable weather conditions? That should address the head pressure issue and let it run for long enough that he can feel confident about what he puts in his inspection report. Especially with a coil that's already wet and somewhat cold, it's hard to find an observable difference in a minute if you switch to heating mode. By five minutes, the discharge air should be getting warm and steamy, though :)
07-07-2006, 06:31 PM
Checking a heat pump in heating mode during the summer is about as dumb as when home inspectors run the water for four hours straight, flood the leetching fields, and say the septic system failed! If it cools right, and the reversing valve switches when stat is turned off, then leave it alone.
07-07-2006, 07:22 PM
Most if not all manufactures do not advise operating in heat mode above 70 deg’s F.
Just list it on your report like the roof.The roof, from ground level appears to be fine.
07-07-2006, 07:28 PM
new construction. in summer, always check cooling then heating.
I know Lennox requires a mild weather kit, when running the heat pump in heating mode above 60F. The kit shuts down the outdoor fan when pressures get to high.
So I never run heat pumps in heat when its 60F+, unless they are setup to do so or Im next to them regulating the head pressure by blocking the outdoor coil.
07-07-2006, 09:37 PM
Originally posted by away822
Will it really show that the heat pump is working?
What do you mean by working? Reversing valve swishing, electric elements coming on for aux. heat, defrost mode stopping outdoor fan motor and swishing back to cooling mode while energizing elements, defrost termination working, em. heat energizing elements while turning off the outdoor unit???
Are you planning on reporting to the home owner all these items?
Please stop saying to have the unit "serviced". That creates pure hell for us contractors. Please tell the seller to have the unit evaluated by a licensed professional at which time other problems may be found.
NO SYSTEM CAN BE SERVICED UNTIL IT IS EVALUATED.
07-08-2006, 03:06 AM
ascj mentioned "...Lennox requires a mild weather kit, when running the heat pump in heating mode above 60F. The kit shuts down the outdoor fan when pressures get too high".
Do must units "above builder grade" like XL14i have such a feature? The reason I ask is - I have the Trane model of the Visionpro with autoswitchover (heat/cool). So, I believe there have been times where the heat might run when it's 65 outside maybe.
So 'short of gas' (humorous username if you think about it), you're saying the units without the mild weather kit would have to rely on the pressure protection switch to avoid compressor damage?
Home inspectors take note - you've got some noted areas for improvement (in your reports !!!):
"Just list it on your report like the roof. The roof, from ground level appears to be fine."
"run the water for four hours straight, flood the leaching fields, and say the septic system failed."
I agree with Steve, using the phrase "serviced" makes it sound like there is a known problem.
The VisionPro stat has a optional outdoor sensor. With the sensor you can program lockout tempatures for your heat pump. So if you have the high lockout at 65 degrees, then any tempature above that will make your backup heat 1st stage and keep the heatpump from running. It also has a low lockout too.
I have never seen a heat pump come standard with any form of mild weather kit, other than a couple of the ductless mini-splits.
Yes, with no mild weather kit you will have to rely on the high pressure switch. Nowdays almost all heat pumps have it setup where the high pressure is on some kinda strike count has far as locking out. So for example Lennox uses 4 stikes before a hard lockout. Alot of the older heatpumps had a manaul reset high pressure switch.
[Edited by ascj on 07-09-2006 at 03:52 PM]
07-09-2006, 04:09 PM
Operation of heat pumps (heat mode) in summer conditions can cause high pressure trips or worse!!!!
I know you have heard this before, maybe if the operational cause is provided you'll have a better understanding.
The outdoor coil is at least 25% larger then the indoor coil, the CFM across the outdoor coil is also at least 25% higher then the indoor CFM. So if you operate a heat pump (heat mode) at warm ambient temperatures, the capacity of the heat pump is above its design.
OK, what does that mean?
The outdoor coil can and will absorb more btu/H than the indoor coil can reject,(the heat pump system picks up more heat then it can get rid of) so the refrigerant system will begin to overheat (high pressure and temperature) this causing the safety trips, if and only if the heat pump has any safeties installed.
If you test in heat mode and the compressor is not protected with safeties, you will cause the differential pressure protection to open, if may not reset and the compressor will need replacement.
Your better off running the heat pump in the cooling mode and testing "operational total capacity" that 18 to 22 delta in the indoor coil is a rule of thumb and means nothing, test you CFM, RAWB & SAWB and find capacity in btu/H, then check that information against the product data or engineering information for that system.
07-10-2006, 01:02 PM
First off thanks for the replies.
I'll try and address some things I read.
Short of actually reading each installation manual, and those are often nowhere to be found, it seems that somewhere around 65F-70F would be the cutoff point. I would rather disclaim it, than break something and try to CMA by saying it failed under testing.
Steve Wiggins: By working I meant producing heat. The trouble as I see it is that running with high ambient temps would not really be a clue whether it will produce enough heat when it is 40F outside. I know a handful of inspectors who suggest to their clients that if it is working in cooling mode then heating mode would be working also. I keep trying to get them to understand that one of these days they will be buying a new system for someone. Only luck has kept that from happening so far.
It is funny you mention using the word evaluated in my report verbiage. I think we are on the same page there. Basically my recommendation comment says to "have a licensed, qualified HVAC professional fully evaluate, service, and/or repair as needed, the heating/cooling system". How does that sound?
ks ftc: Thanks for that explaination it was much more detailed than the limited, "the Freon changes direction in heat pumps" type comments in the inspector books. That does add some credence to my reluctance to run them in the summer. I don't want to be on the hook for the bill should something go wrong.
And I do know the temp splits are a joke. Unfortunately, the TX standards require us to check system functionality by taking them. It is a holdover "standard" from the dark ages and is still being perpetuated with every inspector training class.
I address this in my report by stating that I take the temps only because the state says to and that this method is not recognized by licensed, qualified HVAC professionals as reliable indication of system performance. I then go on to explain that true system performance can only be evaluated by using specialized equipment (i.e. flow hoods, guage sets, etc.) and that this type of evaluation requires a license.
Thanks again to everyone for the information.
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