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    tek's Avatar
    tek Posts: 2, Reputation: 1
    New Member

    Feb 20, 2007, 02:06 PM
    Heat pump and cold weather
    I have a couple of questions about a heat pump. I guess I need to do a little explaining first.

    I have an American Standard air exchanger heat pump with electrical resistance backup. The system has the original mechanical thermostat with separate contacts for the compressor and for the resistance heat. It also has an outdoor anticipator thermistor in the outside compressor.

    The indoor thermostat on my heat pump is always set on seventy degrees.
    When the outdoor temp falls much below thirty degrees, the heat pump's efficiency falls off and it will not heat my house. The compressor and the fan then run all the time.

    When the indoor temp falls about five degrees, the resistance heat kicks in and raises the indoor temp by a couple of degrees and then kicks out again. The compressor and the fan still run all the time.

    The only way to make the compressor and fan cycle properly when the outdoor temp is below about thirty degrees is to manually switch the system to emergency heat.

    Don't heat pump systems have a method of having the heat pump sense the outdoor temp and automatically bring in the emergency heat without the whole system running constantly when the temp is too low for the heat pump to properly function?

    I have studied the diagram of the thermostat and it's wiring, and I have looked the thermostat itself over. It appears that the outdoor anticipator is supposed to reduce the temp difference between the compressor contacts and the resistance contacts in the thermostat. Evidently, not every heat pump has this outdoor anticipator. There are no adjustments that I can see. I have searched the Internet and have found no details of exactly how the outdoor anticipator is supposed to work. I suppose that doesn't matter if I can fix this any other way.

    I have looked at the specs of several of the newer digital programmable thermostats. I have found none that will make use of any outdoor anticipator. None of these thermostats offer anything that would seem to deal with this.

    Isn't there any way to prevent the system from running all the time like this when the outdoor temp is too cold?
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member

    Feb 20, 2007, 02:33 PM
    Everything you said is correct, that is how heatpumps work. There is a way to add a low ambient sensor to the heatpump so it will turn off when it is too cold, Trane calls it restricted mode.
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
    Ultra Member

    Mar 3, 2007, 10:36 PM
    Carrier/Bryant makes a thermostat that lets you adjust the cut in and out temps of the heatpump and gives the outside temp displayed on the screen. It works just about with any system.
    tek's Avatar
    tek Posts: 2, Reputation: 1
    New Member

    Mar 16, 2007, 03:18 PM
    Your answers indicated that indeed some thermostat manufacturers do make thermostats that can respond to outdoor temperature.

    I sent an inquiry to the folks at Honewell. They were very helpful.

    A couple of models of the Honeywell Vision Pro TH8000 series thermostats have a provision for using an optional outdoor temperature sensor. The thermostat can be set up so that when the outside temp falls below a preset level, the heat pump compressor will be locked out, and only the auxiliary heat will operate. It can also be set up so that when the outside temp rises above a preset level, the auxiliary heat will be locked out, and only the heat pump compressor will operate.

    I have installed one of these thermostats and it works quite well. Now the heat pump doesn't run all the time when the weather is below thirty degrees.

    Thanks so much for the advice.
    danwat1234's Avatar
    danwat1234 Posts: 6, Reputation: 1
    New Member

    Nov 14, 2009, 06:04 PM
    Installing a thermostat with a compressor lock-out when the outside temperature gets to a certain temperature below freezing would not save energy costs, most likely. Heat pumps (if in good working condition) will still be much more efficient than resistive heat, down to some temperature below 10 degrees Fahrenheit. This number is from my browsing of datasheets of different heatpump units on the market, so it will depend on the efficient of YOUR unit at a specific temperature.

    You said that the EFFICIENCY of your heatpump drops off when it is much below 30 degrees outside, but I think you meant CAPACITY (BTU's/hr) instead. Good thing about heatpumps in heating mode, they use less power when it is colder outside, so efficiency can still be excellent even though capacity may have dropped by 1/3..

    Why not let the heatpump system run 24/7 when it is below freezing? There is the noise issue..
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
    Ultra Member

    Nov 14, 2009, 06:10 PM
    Man, that's an old post.
    danwat1234's Avatar
    danwat1234 Posts: 6, Reputation: 1
    New Member

    Nov 14, 2009, 06:15 PM
    Quote Originally Posted by KC13 View Post
    Man, that's an old post.
    Haha oops! I haven't done that in a long time. Well, still good info for somebody finding this thread from a search engine.
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
    Ultra Member

    Nov 14, 2009, 06:18 PM
    Whenever I get burned on one of those, I just claim to be "practicing"... :D
    johnmhames's Avatar
    johnmhames Posts: 1, Reputation: 1
    New Member

    Dec 4, 2009, 09:51 AM
    So it is still efficient to run both the aux heat and the compressor, seems like to me that once the temp outside gets below the 20 deg area, it would still be more efficient to run just the aux heat and save the compressor since it would not generate much heat anyhow.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert

    Dec 4, 2009, 10:22 AM
    There is a balance point when it is no longer economical to run the heat pump since the ratio drops down. Now today many heat pumps will still produce good heat down to 10 degrees F and lower but many folks decide they do not want the wear and tear on the outside unit so it lasts longer.
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
    Ultra Member

    Dec 4, 2009, 05:05 PM

    Good timing... I set up a new R-410A system today, set the heat pump lockout at 15 degrees F.
    MargaretteG's Avatar
    MargaretteG Posts: 1, Reputation: 1
    New Member

    Feb 1, 2011, 09:04 PM
    When it get cold do I need to turn on the emergency heat button on my thermostat
    pwooz's Avatar
    pwooz Posts: 1, Reputation: 1
    New Member

    Nov 14, 2011, 10:10 PM
    Honeywell makes a thermostat that has terminals for a outside temp sensor and it can be adjusted to not let the heat pump operate at a user set level it's the 8053 I believe
    tfcheng's Avatar
    tfcheng Posts: 1, Reputation: 1
    New Member

    Jan 23, 2013, 05:32 AM
    An old post indeed. I am glad I found this because similar thing happened to my HP. These days the outside temp drops to 20-10F and my HP can't keep up with the pace. The weird thing is that it always reach a temp that is 2-2.5 F below the target. My thermostat is a 3M-50. I asked the question of how I can reach the target more efficiently, the answer I got is to use AUX heat. What makes me angry is that I just spent almost 4K to install a new 15 SEER Carrier and that still can't take care of my heating in the winter.
    danwat1234's Avatar
    danwat1234 Posts: 6, Reputation: 1
    New Member

    Jan 23, 2013, 06:36 AM
    The 15 SEER rating of your heatpump isn't the capacity. Maybe you should have gotten a higher BTU heatpump, higher 'ton', a ton being 12,000 BTU/hour.

    Yeah the old thermostats and maybe a lot of modern ones too, they keep the heatpump on if the temperature in the house is below the set temperature. If the temperature eventually drops to maybe 2 or 3 degrees below the set temperature, then the heatpump will stay on but then auxiliary heat with be signalled to turn on as well. Sometimes that's a gas furnace, sometimes it resistive (electric hair dryer) heat. That auxiliary heat stays on until the house gets above the 2 or 3 degree gap, but still below the desired temperature. Then, the temperature starts dropping slowly again because the heatpump can't quite keep up. Then after a while the auxiliary kicks in again. The loop continues.

    So to rise the temperature in your house, but also your heating bill, crank that thermostat to ~3 degree hotter than you want.
    mk shields's Avatar
    mk shields Posts: 2, Reputation: 1
    New Member

    Feb 2, 2013, 02:45 PM
    I will give you some basic facts about heat pumps-If they are Geo thermal they can be the best thing that comes with a new house or an old one-but that depends on how old they are? There are many ways a heat pump can be set up,but with your details I can see that certain things were not done-if you have an American Standard Ill bet it doesn't have the system to switch over to aux. heat-you do that yourself-a unit running on and on means it needs work and doest have the switch over system-SWITCH IT YOURSELF-if you can-to aux. heat when it gets around the upper 30,s on down to lower temps. Even the 40,s.-If the outside unit is running on and on its not working anyway and to a point its not cheaper to let it run without any heat coming out of the vents-GO TO AUX-HEAT- cut it down to a nice temp. -its direct heat-and cut it down when it warms up if it doesn't warm up during the day leave it at about 40 and cut it back up when you need more heat-CHECK YOUR RETURN FILTERS-REPLACE OR CLEAN THEM-Heat Pumps set up the right way with electric heat can be very easy on the pocket if its set up right-BUT done wrong it can cost you-SOMETIMES SWITCHING OVER TO AUX. HEAT WILL CAUSE SMOKE BECAUSE THE ELEIMENTS HAVE DUST AND OTHER STUFF ON THEM-OPEN THE DOORS AND LET IT AIR OUT IF IT LAST LONGER THEN 10 TO 15 Minutes. MAKE SURE YOUR HOME IS NOT ON FIRE!! Take-Care,Hope this helps!!
    mk shields's Avatar
    mk shields Posts: 2, Reputation: 1
    New Member

    Feb 2, 2013, 02:47 PM
    Also your T-STAT. can be bad!!
    danwat1234's Avatar
    danwat1234 Posts: 6, Reputation: 1
    New Member

    Feb 4, 2013, 01:09 AM
    Electric AUX heat is very inefficient, leave it off unless the heatpump simply can't keep up. When it is around 40 F or colder, the heatpump will run defrost cycles. During that time (1 to 3 minutes) usually they are set up to tap on auxiliary heat so the air coming out of the vents doesn't get cold. If you want to save some money and if it is electric auxiliary heat, pull the fuses for the auxiliary heat. You don't need it unless it gets something below 30 F.

    Yeah dusty resistive heat coils can be smelly the first time it runs in the winter.
    LadySlipper's Avatar
    LadySlipper Posts: 1, Reputation: 1
    New Member

    Feb 21, 2013, 12:41 AM
    Yes sir, it just helped me immensely! Thank you kindly.

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