Heat Pump question

[starjj]

I had a new heat pump system installed this year. I was reading an article on energy savings this past week and saw something that I didn't understand.

The article stated that if you heat with electric or gas you should turn the furnance down in the evening (like I am use to) BUT that a heat pump system needs to remain on a constant setting????

I have been turning my heat pump system down in the evening because the day setting (67) is just too warm for me to sleep comfortable in. I set it down to 63.

Can someone explain WHY a heat pump system needs to be kept constant? If that is even true.

[TnAndy]

Sure....

Heat pumps have two modes of heat.....the 'regular' version, where they use a compressor outside to extract heat out of the air, and release it inside using freon, and an "emergency" heat option, using a large electric resistance strip heater.....usually 10-15kw.

The normal mode of operation ( compressor/freon ) is quite efficient.....you can get 5-10 times more heat energy inside than you spend in electricity to operate the compressor/fans.

The emergency heat mode is 1-1. You spend 1 BTU of electrical energy to get 1 BTU of heat in return.....it's basically just an electric furnace and not anywhere NEAR as efficient at the heat pump you paid to have installed.

The REASON for emergency heat mode is that IF the outside temps are falling faster than the heat pump can keep up with using the compressor/freon system, the emergency mode kicks in so your house doesn't get cold.....also, if something happens to the compressor, you have a built in back-up....thus the name "emergency heat".

Now...what this means in terms of cutting down your thermostat:

Most heat pump thermostats are designed so if there is a 3-4 degree differential......like say you set it at 63 at night, or when you leave during the day, and you come back later an bump it up to 68 or 70, the heat pump "thinks" you have an emergency situation.....and kicks in the emergency heat....which CAN cost a WHOLE LOT more than if you let the heat pump simply idle along on the same temp setting....this is especially true now days with heat pump efficiencies getting up in the 16 SEER rating range.

SOME thermostats have a little LED light that comes on when emergency heat mode kicks in....if you bump your thermostat up, and see that light kick in, you KNOW you've bumped it enough to kick in that energy hog resistance strip heat.....if yours has that type thermostat, and you can bump it up "just enough" to keep that light from coming on, you would get around that, and do what you are trying to do....but without some kind of indicator ( other than REALLY HOT AIR coming out of the registers ), you won't even know when you kicked in the E mode.

THAT is why the recommendation is you set it and forget it....unlike gas/oil systems where turning it down, then flipping back up in the morning probably did save some energy.

Clear as mud ?

[TnAndy]

Sorry...double post and I don't see a way to delete it....

[Harry Chickpea]

There is ongoing debate about this. In short, a heat pump moves the heat fromt he air outside to the inside of the house. The hotter the air outside, the less it has to work (it is more efficient). When you cut off the pump at night, then the next morning you are trying to warm the air in the house with some of the coldest air of the day. That makes it less efficient and the air coming out of the ducts may seem uncomfortably cool.

What the manufacturers do to alleviate the problem is to use the auxiliary heat source to boost the heat output. That means that if you turn your pump down at night and the temp in the house is 63, when you kick the thermostat up to 70 in the early morning, the resistance electric heat strips or gas furnace will kick in. Resistance electric heat has an efficiency of 1 (1 watt of energy used gives 1 watt of heat out). The heat pump itself is somewhere around four or more times as efficient because it moves existing heat rather than convert it from electricity.

What this all means is that you will end up paying SIGNIFICANTLY more for heating if you don't follow the rules of operation.

There IS an out, if you are willing to take the effort. In the morning, when you crank up the thermostat, listen for when the pump comes on and ONLY turn the thermostat one or two degrees higher. That generally will keep the auxiliary heat from kicking in. Once it goes off, you repeat, and continue doing that until your temperature is reached. It will take longer, but will save money.

An alternate choice you may have if your system is wired to accept it and you use resistance heat for a backup - turn off the breakers for the "electric furnace." That will positively prevent the backup heat from being used. On cold days, you'll need to power it back on.

When heatpumps are operating in temps of below freezing, they get increasingly inefficient, so at some temperature, it may pay to use gas or fire up a woodburner.

THere is a lot more involved, but that is the basic stuff.

[starjj]

Originally Posted by TnAndy

Sure....

Heat pumps have two modes of heat.....the 'regular' version, where they use a compressor outside to extract heat out of the air, and release it inside using freon, and an "emergency" heat option, using a large electric resistance strip heater.....usually 10-15kw.

The normal mode of operation ( compressor/freon ) is quite efficient.....you can get 5-10 times more heat energy inside than you spend in electricity to operate the compressor/fans.

The emergency heat mode is 1-1. You spend 1 BTU of electrical energy to get 1 BTU of heat in return.....it's basically just an electric furnace and not anywhere NEAR as efficient at the heat pump you paid to have installed.

The REASON for emergency heat mode is that IF the outside temps are falling faster than the heat pump can keep up with using the compressor/freon system, the emergency mode kicks in so your house doesn't get cold.....also, if something happens to the compressor, you have a built in back-up....thus the name "emergency heat".

Now...what this means in terms of cutting down your thermostat:

Most heat pump thermostats are designed so if there is a 3-4 degree differential......like say you set it at 63 at night, or when you leave during the day, and you come back later an bump it up to 68 or 70, the heat pump "thinks" you have an emergency situation.....and kicks in the emergency heat....which CAN cost a WHOLE LOT more than if you let the heat pump simply idle along on the same temp setting....this is especially true now days with heat pump efficiencies getting up in the 16 SEER rating range.

SOME thermostats have a little LED light that comes on when emergency heat mode kicks in....if you bump your thermostat up, and see that light kick in, you KNOW you've bumped it enough to kick in that energy hog resistance strip heat.....if yours has that type thermostat, and you can bump it up "just enough" to keep that light from coming on, you would get around that, and do what you are trying to do....but without some kind of indicator ( other than REALLY HOT AIR coming out of the registers ), you won't even know when you kicked in the E mode.

THAT is why the recommendation is you set it and forget it....unlike gas/oil systems where turning it down, then flipping back up in the morning probably did save some energy.

Clear as mud ?

Yes it IS clear as mud lol. Now about the emergency system. The thermostat does shows a setting for emergency operation BUT as I understand it you have to set it to that. I have never seen it just come on even when I bump the temperature up or down.

I think I will call the heating guy who installed the system just to make sure.

Thanks for the explanation

[cfabe]

Turning off the breakers for the heat strips could cause problems... I'm not an expert on these units but aren't those strips sometimes used in the defrost cycle?

[TnAndy]

Originally Posted by starjj

Yes it IS clear as mud lol. Now about the emergency system. The thermostat does shows a setting for emergency operation BUT as I understand it you have to set it to that. I have never seen it just come on even when I bump the temperature up or down.

I think I will call the heating guy who installed the system just to make sure.

Thanks for the explanation

Yep....it has a setting for emergency....but that setting will simply cuts the compressor out of the loop entirely. Say, for example, you notice the compressor unit outside completely iced over....( which could result from a failed defrost switch or low freon, etc )...or you get a HUGE snow, and it covers the heat pump up !!......you could switch the thermostat over to emergency and stop the compressor from attempting to run and damage itself.

However, all heat pumps that have the resistance strip heater ( the "emergency" heater ) built into them ( which is almost all heat pump systems installed in homes ), that strip heater will come on if you bump the thermostat UP more than a few degrees at a time......as I said, you may not notice it other than the air coming out of the register ( especially the ones closest to the air handler unit ) will be a quite a bit warmer than the "normal" heat you get out of a heat pump.

You asked "why".....and the answer is: bumping the thermostat up will cost you more than if you left it alone......as hard as that is to come to grips with for people not used to heat pumps.

[Sawmill Jim]

Cfabe yes in defrost mode it reverses to a c mode and the strips kick it to compensate for the ac being on . At 30fh you are just as well off running the heat strips only because balance point in almost reached . Some here are going to the duel fuel heat pump it uses gas in place of strips and locks out the compressor at a set outside temp say 34 degrees and heats with gas only .