Does cooling require more BTU/hr than heating to maintain same temp difference?

[AC/DCdude17]

X-No-Archive: Yes

Well, my 5,000 BTU(1.5kW cooling) air conditioner struggled to maintain

75°F when it was 100°F outside. The compressor ran continuously and it simply will not pull down a small room below 75°F and it took a long time to get down to 75°F.

My portable space heater which is also 5,000BTU/1.5kW can maintain 72°F just fine when it's 30°F outside and it doesn't have to run continuously.

How come my A/C struggles to maintain 25°F difference running continuously whereas my heater can maintain 40°F+ difference without running continuously even though they both have the same BTU performance?

Both results were with the central HVAC turned off.

[Joseph Meehan]

No, but you are failing to consider the heat gain that normally takes place winter and summer.

Winter or summer you have lights (all add heat as well as light), water heater, adds heat inside you home, windows generally create a net gain of heat both summer and winter, almost all electrical devices from the door bell to your computer add heat all year, even you add heat when you are home. During the day in both winter and summer, the outside of you home (roof and walls) are heated during the day and that increases heat gain. Now add to the fact that your A/C not only cools the air, but dehumidifies it and you can see why it takes more BTUs to keep you home cool in summer as it takes your heater to keep it warm during the winter, with equal temp differences.

Generally a good install will call for a closer match of A/C size than heat because the A/C will dehumidify less well if over sized.

[Edwin Pawlowski]

You have only once source of heat removal (cooling) with the AC, but you have many heat sources helping the space heater.

The AC is pulling down the air temperature and heat is still getting into the room from various sources. The walls not only tot he outside, but to the rest of the house are transmitting heat into the room. The crack under the door. Lights, TV, even your body. IIRC, an average adult gives off 400 Btu per hour just sitting in a chair.

The heater is getting help from all of these sources. Daylight hours it is getting solar heat. While the outside temperature is 30 degrees, what about the rest of the house? Are all the walls at 30 or are they closer to maybe

60 giving a lesser differential and thus lesser heat loss?

While 5,000 Btu is still 5,000 Btu, the heating and cooling loads are not necessarily equal in the particular room. Ed

[nicksanspam]

And specs for heating equipment are more straightforward than specs for cooling equipment. An AC may only make 5K Btu/h of cooling under rare operating conditions.

Nick

[Richard J Kinch]

Heat load is more than just temperature difference.

[PrecisionMachinisT]

performance?

Only sorta slightly related, but Im running a water source heat pump, cooling house and heating swimming pool concurrently......

Water flow rate is ~7 gpm, incoming water is at 84 deg F, outgoing at 96 deg F--so I'm figuring it's moving roughly 40,320 btu of heat--this is a 3-1/2 ton unit.......

Anyone care to double check my numbers or have any questions / comments ???

[PopRivet]

struggled to

compressor ran

small room below

5,000BTU/1.5kW can maintain

have to run

difference running

difference without

same BTU

Good grief, there are certainly a lot of "logic" answers here, most with some but not much merit. Simply stated, it takes a LOT more energy to drop the temp a degree than to raise the temp a degree, because of the methodologies. The technology for increasing temperature is simply much more efficient that that for lowering the temperature.

Pop

[jriegle]

You should feel fortunate that little unit can maintain that temp differential. It must be working hard. I know you like to experiment so put an amp meter on it to see. Compare with cooler outside temps. John

[Edwin Pawlowski]

Explain please.

If you have a mass and remove 5,000 Btu or add 5,000 Btu, it is still the same amount of energy it is still the same mass. Since Btu is really an expression of Btu PER HOUR, the same amount of energy is being moved in the same time period.

Take the window AC unit and mount it backwards so it exhausts from the condensing coil the heat into the room. Would the effect of running it raise the temperature more or less than a heater that gives of 5,000 Btu of heat? If two rooms were the same temperature and one had the heater, the other h ad the AC (assuming the outside air is at the temperature used to get the 5k rating), which room would be heated more?

[PrecisionMachinisT]

Doh!!!

Stop it NOW.................

Your gonna confuse them all with this talk of "btu's"....

[nicksanspam]

I'm afraid you are incorrect, Mr. Rivet. Think "COP = 3."

In wintertime, with the cool side in a damp basement stairwell...

About 30% more than 5000 Btu/h, given compressor and fan motor powers.

Nick

[Pop Rivet]

it is still the

Btu is really an

being moved in the

exhausts from the

of running it

gives of 5,000 Btu of

the heater, the

temperature used to

True, but the LOSSES (efficiency) of causing that are grossly different. Your analogy is sound, but it ignores the losses involved in makng that change occur, which is what the OP was asking about. I'm afraid getting into a technical debate, especially one with the lossless descrip you're trying to use would be futile and take way too much ether and time. Keep reading; it's there.

Pop

[Pop Rivet]

the

=== I'm afraid I don 't understand: After making that comment, youthen proceed next to agree with it by offering a related analogy. ?!?

exhausts from the

stairwell...

or less than

motor powers.

[Edwin Pawlowski]

I'm not looking to get into a debate, but I'm looking to learn something. Guess you don't know enough to teach me so I'll look elsewhere. Thanks anyway. Ed

[John Cochran]

Think about how your space heater works vs how an air conditioner works. The space heater: Electricity in - Heat out. The amount of heat generated is independent of the outside temperature. So the space heater only has to make up losses. The amount of heat generated is only due to the electricity coming in.

The Air Conditioner. This little device doesn't "generate cold". What it does is move heat from one location to another. But heat only goes from hotter to colder. So if it's 100 degrees outside and you want it to be 75 degrees inside, you have a problem. You need to make something colder than 75 degrees inside and make something hotter than 100 degrees outside. The air conditioner works as follows: 1. Compress the refrigerant gas. Some high school physics will show you that you now have made the gas hotter. In an ideal world, if you now released the pressure on this compressed gas, you then get some uncompressed gas at its original temperature. But that isn't what's done. 2. Pass the hot compresses gas through a heat exchanger. This heat exchanger is outside and the hot gas becomes cooler. Note: The rate of cooling of this hot gas is dependent on the temperature difference between the hot gas and the outside temperature. If it is very hot outside, then the hot compressed refrigerant isn't cooled as efficiently as if it's colder outside. 3. Now take the cooled refrigerant which is now a liquid and allow it to boil under a lower pressure. This "boiling" takes heat from the environment. This happens in another heat exchanger inside the house. 4. Go back to step 1 with the low pressure refrigerant gas.

The key thing to note is that the process become less efficient when the outside temperature rises. The air conditioner is effectively attempting to heat up the outside air. So when the temperature rises, two bad things happen: 1. The air conditioner has to do more work due to heat gain from the outside to the inside of the house. 2. The actual process becomes less efficient because the outside heat exchanger can't work as well because the temperature difference between the hot compressed refrigerant gas and the outside air is less.

For your space heater however, when it gets colder the problem is: 1. The space heater has to do more work due to heat loss from the inside to the outside (the same as problem 1 for the air conditioner except in reverse). But, the space heater doesn't lose efficiency just because it's cold outside.

Hope this helps explain things, John Cochran

[AC/DCdude17]

So, Newton was wrong?

The technology for increasing

This is the biggest non-sense posted in my thread.

Space heater can only output as much heat as the electricity going in and this will not change. Simple law of conservation of mass.

Cooling is more efficient. You can take about three units of heat from inside and take it outside with one unit of electricity. The condenser will spit out three units taken from inside + one unit used by the compressor.

[Doug Miller]

What does Newton have to do with this? Possibly you're confusing the three laws of thermodynamics, with Newton's three laws of motion.

Not at all -- he's absolutely right. You need to go back to school.

Heating is more efficient than cooling for two reasons: First, *all* mechanical processes eventually dissipate *all* their energy as heat. Thus the energy input into a heating device is all converted to heat. So is the energy input into a *cooling* device.

Second, the laws of thermodynamics work in favor of heating, and against cooling. The temperature gradient is downhill for a heating system, and uphill for a cooling system. Simply put, a heating system transfers heat from a warm object (e.g. a furnace) to a cool object (e.g. a room); this transfer occurs spontaneously. A cooling system, OTOH, transfers heat from a warm object (a room) to a *hot* object (the outdoors -- obviously it's hotter outside than inside, otherwise why are you running your air conditioner?). This transfer does *not* occur spontaneously, and requires additional energy to force the heat transfer uphill.

Actually, that's "conservation of *energy*".

Speaking of nonsense... you just won the prize. Cooling is *far* less efficient than heating.

[nicksanspam]

No. The electrical energy into an AC moves about 3X more cooling energy.

Nick

[Doug Miller]

So you're saying that air conditioners operate at an efficiency of 300% ?

Sorry, I don't buy that.

There isn't any such thing as "cooling energy" anyway. "Cool" is the absence of heat. An air conditioner does not create "cool". It moves heat from inside the house to outside the house. This is an uphill temperature gradient, and is guaranteed to be a less efficient process than heating a home, which moves heat on a downhill temperature gradient from a warm furnace to a cool room.

[PrecisionMachinisT]

Then suggest you look at the nameplate ratings then--and note that while the heater draws ~ 1500w, while the A/C likely only draws ~ 500w

I run heat pumps here year round.......when the outdoor temps drop below 40 deg F, heat pumps drop off in effeciency, and so the backup electric heat strips kick in--when this happens, my electric bill also about triples..........