watts=btu's ??

[Besoeker]

Trade jargon is often imprecise. For example, we often say "power" when we mean "energy". However, when converting units we should be exact and not leave anything to chance regardless of what Wiki says.

I totally agree.
Say what you mean otherwise people will think you mean what you say.

 

[don_resqcapt19]

... There is an efficiency factor to take into account, in the transfer of energy from electrical to heat. For example, with an 80% efficiency factor, a heater that draws 1500 watts from the electrical system might deliver no more than about 4000 BTU?s per hour of heat into the room.

Charlie,
What form does this loss of efficiency take in an electric heater? Most of the efficiency losses in electrical systems result in heat and that really wouldn't be a loss if you are trying to make heat.

 

[LarryFine]

Most of the efficiency losses in electrical systems result in heat and that really wouldn't be a loss if you are trying to make heat.

That's why electric heat is efficient, even if it is expensive.

 

[charlie b]

I was speaking in general terms about the concept of unit conversions. You can't always say that a watt of electrical energy equates to a watt of heat delivered to the room, nor for that matter would it equate to a watt of work delivered by an attached pump or an attached drive belt.

Not all heaters are 100% efficient in turning electrical energy into heat. Not all heat makes its way into the room into which you want heat. In this specific case, a "toe kick heater" that (1) is located in the room you are trying to heat and (2) does not involve a fan, a compressor, a heat exchanger, or any part of the air conditioning cycle will be essentially 100% efficient. By contrast, a "heat pump" located outside the house will not.

 

[rattus]

Pick on Charlie B. Day:

Pick on Charlie B. Day:

I would argue that one cannot measure "efficiency" of a heat pump because it does not convert electrical energy into heat. It merely pumps heat from one area to another. If we compute "efficiency" of a heat pump, we find that it is greater than one.

Now a gas furnace exhibits an efficiency less than one because some of the heat escapes up the flue. Perhaps 90% makes it into the rooms. No flue with electric heat, so it should be 100% efficient.

 

[charlie b]

I would argue that one cannot measure "efficiency" of a heat pump because it does not convert electrical energy into heat.

Yes it does. The thing that gets delivered to your house, when you order a "heat pump," includes not only the fan that moves heated air from outside to inside, but also the device that causes the air to get heated in the first place.

In any event, I would argue that we usually define a thing's efficiency in terms of the system as a whole. I would define the efficiency of a heat pump in terms of the heat delivered to the room(s) it serves, as compared to the electrical energy required to operate it.

 

[gar]

080925-1330 EST

charlie b:

I believe the original question was about a resistance heater.

For the reference of others -- a heat pump working from a reasonable heatsink (the earth at 55 deg) has an efficiency greater than 100% relative to the electrical energy in vs the heat out.

.

 

[charlie b]

I believe the original question was about a resistance heater.

No, it was about unit conversions. The example employed was a resistance heater, but the notion of unit conversion extends beyond that example.

For the reference of others -- a heat pump working from a reasonable heatsink (the earth at 55 deg) has an efficiency greater than 100% relative to the electrical energy in vs the heat out.

But the overall efficiency, taking into account all energy in and all energy out, is less than 100%. Or has someone finally invented the perpetual motion machine? :roll: :grin:

 

[jghrist]

Yes it does. The thing that gets delivered to your house, when you order a "heat pump," includes not only the fan that moves heated air from outside to inside, but also the device that causes the air to get heated in the first place.

I disagree. A heat pump moves heat from the outside air into the inside. If efficiency of a heat pump is measured by heat supplied to the inside (converted to kWh) divided by the kWh input to the heat pump and air handling unit, you would get an efficiency over 100%. Ain't no such thing.

It is better called a coefficient of performance.

 

[weressl]

Yes it does. The thing that gets delivered to your house, when you order a "heat pump," includes not only the fan that moves heated air from outside to inside, but also the device that causes the air to get heated in the first place.

In any event, I would argue that we usually define a thing's efficiency in terms of the system as a whole. I would define the efficiency of a heat pump in terms of the heat delivered to the room(s) it serves, as compared to the electrical energy required to operate it.

...and that would include the latent heat derived from the ground on the ballance sheet.

100% efficiency is always present as energy do not disappear, nor does it gets created. Directing the converted energy to the intended use is what we are talking about and thge most efficient systems are probably electric motors where up to 95% of the electrical energy can be converted to emachanical energy, but then the efficiency greatly degrades in the mechanical equipment such as pumps and fans in terms of how much material they can move.

 

[winnie]

The thing that gets delivered to your house, when you order a "heat pump," includes not only the fan that moves heated air from outside to inside, but also the device that causes the air to get heated in the first place.

A heat pump consumes a certain amount of electrical energy, and delivers a certain amount of heat energy to the home. Energy is energy, and you can take a ratio.

As a wee one, I was soundly berated for using the term 'efficiency' in the above situation. It was suggested that I use 'performance' or some other term that makes it clear that you are only comparing the ratio of inputs and outputs that you care about or are paying for, rather than _all_ of the inputs and outputs of the system.

-Jon

 

[rattus]

A heat pump consumes a certain amount of electrical energy, and delivers a certain amount of heat energy to the home. Energy is energy, and you can take a ratio.

As a wee one, I was soundly berated for using the term 'efficiency' in the above situation. It was suggested that I use 'performance' or some other term that makes it clear that you are only comparing the ratio of inputs and outputs that you care about or are paying for, rather than _all_ of the inputs and outputs of the system.

-Jon

Yes, but the proper term is "efficacy" in such a case. Still, the HVAC folk use "SEER" which is a ratio of BTU/hr to KW, and they call it an "efficiency ratio". I was taught that "efficiency" can never be greater than one.

 

[gar]

080925-1710 EST

From a customer's point of view the interest in a heat pump its ability to put more heat (KWH) into his home than electrical input (KWH) into the heat pump. Efficiency in the general sense is a perfectly valid word to describe this ratio when you define what are the inputs and outputs in the ratio.

That energy that is present in the ground and is pumped into the house is free to the home owner other than for the capital outlay and the electrical energy input to the heat pump. This is not a perpetual motion machine. It does not produce more energy than all of the inputs, but part of the input is no cost to the customer.

.

 

[dbuckley]

Yes, but Wp is not always correct, so how can one know when WP is correct or fabricated?

One cant, except by checking multiple sources.

But a bit of research carried out found that WP had the same percentage of errors as the Encyclopaedia Britanica. So although universities dont allow it as a referencable source, for the rest of us, its pretty good.

 

[charlie b]

But a bit of research carried out found that WP had the same percentage of errors as the Encyclopaedia Britanica.

I don't suppose that that particular bit of research was carried out by way of a reading of WP? :grin:

 

[tuffgrunt]

Heat pumps have efficiency ratios in excess of 2 or 3, whereas electric heating has an efficiency ratio of 1. The reason heat pumps have these efficiency ration is because the heat pump is extracting heat from ambient sources. The heat pumps efficiency is dependent upon the temperature of the ambient heat of the source where the heat is being extracted. Some heat pumps use the air for a source of heat and others may use water(ponds, water tanks, underground water) or from the heat of the ground several feet below the surface.

Heat pumps become less efficient in extremely cold environments and usually do not perform well in subfreezing climates, where electric strip heat may have to be used to augment the the BTU input from the ambient heat source.

 

[weressl]

Yes, but the proper term is "efficacy" in such a case. Still, the HVAC folk use "SEER" which is a ratio of BTU/hr to KW, and they call it an "efficiency ratio". I was taught that "efficiency" can never be greater than one.

Efficiency is the proper term in this case. Efficacy refers to a produced effect, not conversion from one form of energy to another form of energy. Efficacy of lighting refers to the lumens produced poer units of energy, efficacy of medical treatment refers to the degree of healing a treatment can produce.

Main Entry: ef?fi?ca?cy Pronunciation: \ˈe-fi-kə-sē\ Function: noun Inflected Form(s): plural ef?fi?ca?cies Date: 13th century : the power to produce an effect

Main Entry: ef?fi?cien?cy Pronunciation: \i-ˈfi-shən-sē\ Function: noun Inflected Form(s): plural ef?fi?cien?cies Date: 1633 1: the quality or degree of being efficient2 a: efficient operation b (1): effective operation as measured by a comparison of production with cost (as in energy, time, and money) (2): the ratio of the useful energy delivered by a dynamic system to the energy supplied to it