Space Heating

Heat pump is what I think they call t. Very common.

If you already have a central heating system and still freeze, you may have a number of problems adding up. For example, if it is really cold (not this year ...) you may have to better insulate, cut air leaks, check windows and doors weather strips, electrical outlets on exterior walls not scealled, etc. I did some testing. I have a nasty steel insulated ... exterior door. at -30 f it was a source of cold, i used an infrared parabolica and placed it at about 5 feet from the door and had at least 2 feet around it. It cut cold dead cold, added comfort. In front of one patio door, i have floor water Rehau tubing heating. Also, I am designing an infrared ceiling heating solution in front of my second patio door. They are 2 ft x 4 ft sheetrock heating boards, you can put them behind your finish sheetrock or even leave them apparent, you can use as many as you want. This is likely the best comfort solution. If you want more info, i will send you their coordinates. YC

The system you refer to is a reverse cycle refrigeration system, commonly called a heat pump. Through a series of solenoid valves, the flow of refrigerant is reversed between the evaporator coil and the condenser coil, such that the hot refregerant gas from the compressor is pumped through the evaporator coil, heating the indoor air as it is blown across the coil. After which the pressure and temperature of the refrigerant is reduced, causing the refrigerant to change to a liquid. It is now colder than the ambient outside air; hence through the condenser coil which allows the refrigerant to pick up heat from the outside air, turning it to a gas before entering the compressor, and repeating the cycle. This particular system is called an air to air heat pump. Other systems use water or other mediums in the condenser and evaporator systems, to produce the same effect.

OLD F**T

As stated in other posts, you have described a heat pump.

They are more efficient than resistance electric heaters (which are 100% efficient in converting electricity to heat, but an electric heat pump moves heat from the outside, making it far more than 100% efficient when compared to converting the same amount of electric power to heat).

The problem with the air to air heat pumps is that the colder it is outside, the less efficient they are and when the outside air drops to somewhere in the neighborhood of 4-7°C, the compressor shuts off and heat is then supplied by an incorporated gas or conventional electric heater, which can also function as a booster when needed. The exact temperature where the compressor will shut down depends on the design parameters of the unit, regarding compressor, evaporator and condenser specs, refrigerant type and pressures, throttling valve, "freezostat" etc. Some have been designed to operate even below 0°C, but the added complications and reduced efficiency make them rare. No point in running the machinery (except for the interior blower) to gain little or nothing over straight resistance coils. This is why many heatpumps extract heat from the ground, or groundwater rather than the air. The outside air heat extraction type are most useful and common in areas of mild winters.

"More than 100% efficient" may need qualifying.

Heat-pump systems are characterised by a "coefficient of performance" [CoP]. A CoP of 2.5 means that for every 1kW of electrical energy consumed, one receives the equivalent heating effect of 2.5kW. One might be tempted to describe such a system as 250% efficient. Conservation of energy may infer that "efficiency" is the wrong term to use.

One can't get anything for nothing. If one wants something to go uphill, one must push.

You are absolutely correct in your explanation, lest some people be confused by my words as you were.

However, I DID qualify it:

"(which are 100% efficient in converting electricity to heat, but an electric heat pump moves heat from the outside, making it far more than 100% efficient when compared to converting the same amount of electric power to heat)."

There isn't much detail here. I will assume you are referring to a window-mount type air conditioner. In this case, practicality may dictate the answer more than efficiency.

First, the plug on these air conditioners is on the cooling side of the air conditioner. Second, the air filter is on the cooling side of the air conditioner. Third, the controls are on the cooling side of the air conditioner. The cooling side of the air conditioner is not weather-resistant while the condensor is. Finally, you will need to modify the thermostat control as it will be attempting to cool the outside instead of heating the inside.

For these reasons alone, I suggest trying to reverse the cycle as opposed to turning the unit around. However, an easy option that is much less efficient would be to bring the entire unit inside and run it as is. It will surely heat in a closed environment (and de-humidify the air) but you will still need to modify the thermostat control as mentioned above.

Considering all the above modifications you will need to make, I would suggest purchasing a space-heater. You will probably save money, time, and effort in the long-run.

Guest #5 was tempted to say that a heat pump with a CoP of 2.5 was 250% efficient, and that would be correct, because efficiency is always a relative term. By the definition he gave, that heat pump is 2.5 times more efficient than an ideal electric heater, which operates at !00% efficiency, the standard for turning electrical energy into heat. You cannot compare electric heaters to gas and oil furnaces, except on a cost basis, BTU per $, if you know the BTU (British Thermal Unit) output, energy source usage, and energy source cost rate. Of course, there are metric equivalents to the BTU (as well as other currency besides the US $), but I am not sure which is used in heating.

I wonder how efficient a window air conditioner, set inside as you described, would be in comparison. Is any energy lost by any other means than heat? Well some units are quite noisy, so some mechanical energy is lost through sound dissipation beyond your heating space, but it should be very small. The same goes for any vibration that might be transmitted through the floor. Actually, the greatest non-heat loss with any electric motor driven system would be the power factor. This is not a real energy loss, but it might as well be, because you are charged for it anyway.

Maybe an EE could explain it better, but what happens is that a motor is basically a big inductor, and it pulls voltage and current out of phase with each other. Since the power company monitors voltage in and amp-hrs. used, while they say they are charging by the kilowatt-hr (Power=Voltage x Curent, Energy=Power x Time) for energy, they are really charging by the kilovolt-amp-hr (KVA-hr.), since they are multiplying separate peaks (or actually the out of phase RMS values of voltage and current), while what your motor uses instanteously is actually the instantaneous voltage x current, which should give a lesser value accumulatively since one is almost always lower than the other. Where does this "energy" go? Why, right back to the power company, which uses a practice called "power factor correction" to bring voltage and current back into phase by adding capacitors to offset the inductance.

Large users of motors and other inductive power loads (solenoids, inductive heaters, radio transmitters, etc.) also use power factor correction to limit this financial loss. I believe there are also small consumer units, usually called "energy savers", that plug into the wall between the outlet and inductive loads like A/C, refrigerators, freezers, washing machines, etc. I think they claim to save anywhere between 5-15% on your "energy" usage for each appliance.

The suggestion to purchase a space heater is a good one. It might be best to do a cost analysis before you plunge into any new equipment, though. You might find a small gas furnace (natural gas or bottled propane) to be incredibly cost effective, if gas prices are low in your area. If you had a cheap source of waste oil (petroleum or vegetable oil) an oil-burning unit might be best. Otherwise, an efficient electric heater might be best for supplemental heat, or replace your A/C unit with one that has a heat pump function. I doubt that setting your window A/C unit inside would be very cost effective in comparison!

I doubt the OP meant turning a window air conditioner around: that would be too silly as you pointed out.

But, your suggestion is equally silly, if you were serious:

"However, an easy option that is much less efficient would be to bring the entire unit inside and run it as is. It will surely heat in a closed environment (and de-humidify the air) but you will still need to modify the thermostat control as mentioned above."

You would very rarely ever want to heat and dehumidify the air for living space, since the very act of heating it reduces the relative humidity. But you have neglected the fact that window mount ACs have a shallow condensate pan (how would you empty it?) plus they use a variety of means to spray as much of the condensed water on the condenser coil as possible to increase efficiency, so that water would end up back in the room. Other than the latent heat of vaporization (and you don't really want to dehumidify the air if you could) the only other heat added to the room is the electrical power the AC consumes. So why even consider it at all?

You have created a very expensive and complicated electric heater for no valid reason. If you want electric heat, get an electric heater, which is where you yourself end up.

If you meant the AC in the room thing "tongue-in-cheek", then I'm off base and apologize; I am a fan of subtle humor.

Ironically, the "A/C heater" could be very efficient. As you pointed out, "the only heat added to the room is the electrical power the A/C consumes". Or put another way, the electrical power that the A/C consumes is added to the room as heat. Yes, efficient, but NOT effective! One might need dozens of these "very expensive and complicated electric" heaters to put out the same heat as a small ceramic or wire element heater.

This points out a very serious problem when people focus on "efficiency" when choosing appliances. Our government does the same thing when they mandate efficiency. My highly efficient low water-usage toilet is very efficent in its water usage, per flush, but highly ineffective, since I usually require many more flushes per sit-down, else I end up with a clogged toilet that also requires many more flushes to unclog.