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Heat Pump Performance When Cold Outside ???
I need an expert out there to tell me if my heat pump is working properly. Outside temp is 27 degrees. Indoor ambient air temp (read from both thermostats) is 66 degrees. Thermostat is set to 68 degrees. Heat pump seems to run and run for long periods, in some cases hours on end with very little increase in temperature. In fact, vent temp reading with my laser thermometer is 69 degrees, no wonder it's not improving much.
If I bump the thermostat to anything 3 degrees or more above the current ambient air temp (in this case setting it to 69 degrees), a little "aux" symbol appears, which I presume to mean there is a toaster grid somewhere heating up (this of course means $$$$). When aux is indicated, the vent temps shoot up to 89 degrees within a minute or so. At this point, within 20 minutes the ambient air temp will rise about 1 degree, which then shuts the aux feature off, and the cycle continues with the fan blowing for the next hour or so until the temp again drops enough to invoke the aux feature. Is this behavior normal? My rather crude understanding of a heat pump is that it "reverses" function in order to remove heat from the air outside the house and release this heat into the inside of the house via the furnace blower. Sort of like a reverse air conditioner. Am I right? If so, logic would dictate that efficiency would drop off sharply as the temperature outside drops, since there is very little heat to remove from the outside air. But this seems a little out of the ordinary. In fact, I don't remember it behaving this way last year. But then again, I don't think 27 degrees is normal for North Texas (Chicago transplant, still figuring out the weather here). Does this type of operation sound normal, or should I schedule an appointment with an HVAC guy? Are there some simple things I can check myself before doing so? Thanks in advance!
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08 W251 R350 97 W210 E320 91 W124 300E 86 W126 560SEL 85 W126 380SE Silver 85 W126 380SE Cranberry 79 W123 250 78 W123 280E 75 W114 280 |
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By the way, we are using those oil-filled radiator type electric heaters on a low setting in the bedroom overnight. They are great for taking the chill out of the room. But I have no idea what they are doing to my electric bill. In fact, they worked so well last night that I tried shutting off the central heat pump, since it seemed to be running and running with no end in sight and very little heat output. Big mistake - it was 58 degrees this morning when we all got out of our rooms. But I worry that the heat pump might run all night and just incur some ungodly electric bill!
Any thoughts?
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08 W251 R350 97 W210 E320 91 W124 300E 86 W126 560SEL 85 W126 380SE Silver 85 W126 380SE Cranberry 79 W123 250 78 W123 280E 75 W114 280 |
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It's an interesting topic, wish I had good answers for you.
I've been looking at and thinking about absorption cooling system for a while now, that's the process that propane refrigerators use. Getting your head around the thermodynamics of it is surprisingly tricky. I'm guessing that a heat pump in the cycle you're talking about sends coolant out at say, 0 degrees F and has it returned at 27 F. If the pressure in the system is right which by design, it would be, at that temp. some condensation would take place, which would (should) give off heat. I can't quite get my head around it. I can figure it the other direction, but in reverse it clouds up. Howstuffworks claims that in climates that spend time below freezing, a heat pump is not necessarily more efficient than other types: http://home.howstuffworks.com/how-to-troubleshoot-a-heat-pump.htm
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1986 300SDL, 362K 1984 300D, 138K Last edited by cmac2012; 01-02-2008 at 11:27 PM. |
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Make sure it does a defrost cycle every now and then. In certain conditions, the coils outside can get iced up - there is a cycle that is supposed to melt that stuff off. Good airflow is important too, so it can suck every last bit of heat out of the surrounding area.
But..once it gets that cold, it's struggles to give you heat. The heatstrips ought to come on, once the pump can't hack it. (besides when you turn up the thermostat past 2-3 degrees above current room temp). Having the heatstrips do their thing for 20 mins. might use up around the same amount of electricity as the pump running for an hour and 20 mins. It is 39 here right now, and it heated my house up a degree (70 ->71) in about 15 mins.
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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein 09 Jetta TDI 1985 300D |
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I used to know the temperature below which an air to air heat pump is no longer effective. It may be 32 degrees faranheit. After that you need to use the toaster coils to get heat. Yes, they are expensive to operate. The space heaters you have are the same effeciency as the strip heaters but have the advantage that you can just warm the areas where you actually are....so they will consume less energy than heating the entire house to the comfort zone.
Good luck....at least in Texas it is not likely to last long. Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC] ..I also have a 427 Cobra replica with an aluminum chassis. |
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The efficiency of a heat-pump ends below exterior ambient temperatures at or below 32'. Your interior furnace's infra-red coils do the heating below that point. Above 32' they're excellent. Your latitude is not bad as a heat-pump heating source. Further south is even better.
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It sounds like your aux heat isn't kicking in automatically when the outside temperatre drops very low. I don't think most heat pumps are designed to operate effectively when ambient temps are at, or below, freezing.
20 years ago, my foks installed a 'dual-fuel' heatpump system in their Virginia Beach home, which uses an oil furnace as the aux heat, instead of a resistance heater. When the outside temp drops to about 36 F, the system automatically switches to oil heat. Also, if it's above about 36 F, where it would normally be running on the heatpump, but one wants to boost the inside temp a few degrees by nudging the thermostat, the system switches to the oil heat temporarily to quckly raise the temperature. (Sounds like this part of your system is still working, except for the difference in aux systems) Once the higher setting is reached the heatpump takes over until the outside temp drops below about 36 F. There's also an 'emergency heat' switch on our thermostat. If the heatpump fails, it allows heating with just the oil furnace. Sounds like possibly a temp sensor/circuit in your outside compressior-condenser unit isn't working. If you have an aux heat setting on your themostat, you may have to monitor the outside temp and switch it on accordingly until someone can check out the heatpump. Happy Motoring, Mark
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DrDKW |
#8
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A good wiki link on Heat Pump operations Clicky
Quote:
Quote:
The manufacturer should have all of this built into the temperature sensors, and it should bring on the 'toaster' only when needed. The only way to tell would be to put a kilowatt-hour meter on the unit, and compare hourly consumption with a steady outdoor temperature. |
#9
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Heat pumps suck! The point at which they no longer warm the air is when it gets cold . . .
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" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century OBK #55 1998 Lincoln Continental - Sold Max 1984 300TD 285,000 miles - Sold The Dee8gonator 1987 560SEC 196,000 miles - Sold Orgasmatron - 2006 CLS500 90,000 miles 2002 C320 Wagon 122,000 miles 2016 AMG GTS 12,000 miles |
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Water to air heat pumps do a lot better. Instead of trying to take heat from the air which is at 27 f they will be taking heat from the ground which if deep enough will be as warm as 50 f.
The most effecient type is the open loop type which takes water from a well and discharges it into a stream or lake, or into a second well so that it does not deplete the water table. It sounds as if the OP's heat pump is working normally. Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC] ..I also have a 427 Cobra replica with an aluminum chassis. |
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Quote:
Happy Motoring, Mark
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DrDKW |
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I seem to remember him saying that he was deliberately setting the stat so that it never kicked on. See his middle paragraph.
Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC] ..I also have a 427 Cobra replica with an aluminum chassis. |
#13
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Quote:
Happy Motoring, Mark
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DrDKW Last edited by Mark DiSilvestro; 01-03-2008 at 08:22 AM. |
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Anyway, get an electric blanket and shut the heat off. Or like I do set it at around 62 - 65 degrees. I have one of those oil filled heaters and they work great. Using electric heat it takes the same amount of BTU's to heat a room if your using a radiator or forced air. Just heating the bedroom with electric heat is less costly that heating the whole house by any means. Danny
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1984 300SD Turbo Diesel 150,000 miles OBK member #23 (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination |
#15
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Quote:
Happy Motoring Mark
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DrDKW Last edited by Mark DiSilvestro; 01-03-2008 at 01:00 PM. |
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