Question about the practical benefits of heat pumps

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Low-Q
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Hi,

I did read an article (Norwegian one) about heat pumps. Several owners claims that the annual costs for operating a heat pump versus a traditional electric stove isn't much different. Even if the heat pump isn't reversed at hot days in the summer (And used solely for heating), these owners say that the cost might also be slightly higher than using electric stove. Also even if the average temperature inhouse isn't changed.

So my questions are: Are these COP numbers not real? Are they in practice about 1 or less?
It appears to me that the technology isn't as efficient as I thought it was.

Do you have theories or facts that supports these claims?

Just good to know before I decide to install a heat pump.

A quote using google translate:
"Now an analysis from Statistics Norway (SSB) that heat pumps may not be as environmentally friendly as you thought. If one is to believe SSB, they contribute at least not to lower the overall power consumption.

Households with heat pump has in fact on average about the same power consumption as other households, it is going ahead SSB analyzes 2/2013."

Br.

Vidar
 

Answers and Replies

  • #2
SteamKing
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I don't know how hot it gets in Norway during the summer, but try cooling your house with an electric stove.
 
  • #3
DrClaude
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Several owners claims that the annual costs for operating a heat pump versus a traditional electric stove isn't much different.
What does that mean? Do they include the cost of the pump itself, and if yes, amortized over how many years?

In my own experience (although in Sweden, not Norway :wink:), a heat pump (geothermal) uses much less electricity than an electrical water heater. But when taking into consideration the cost of the pump, and maybe a 15 year lifespan, it is indeed close to break even in terms of money at current costs for electricity. I still think it is worthwhile, especially with expected increases in the cost of energy.

A quote using google translate:
"Now an analysis from Statistics Norway (SSB) that heat pumps may not be as environmentally friendly as you thought. If one is to believe SSB, they contribute at least not to lower the overall power consumption.

Households with heat pump has in fact on average about the same power consumption as other households, it is going ahead SSB analyzes 2/2013."
For the first part, maybe, if you count the manufacture of the heat pump. For the other quote, "Households with heat pump has in fact on average about the same power consumption as other households", are they comparing on average, or comparable houses? Because I assume that there is a very strong bias here: you are more likely to invest into a heat pump if your energy use is already high and you want to bring it down.
 
  • #4
ZapperZ
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Hi,

I did read an article (Norwegian one) about heat pumps. Several owners claims that the annual costs for operating a heat pump versus a traditional electric stove isn't much different. Even if the heat pump isn't reversed at hot days in the summer (And used solely for heating), these owners say that the cost might also be slightly higher than using electric stove. Also even if the average temperature inhouse isn't changed.

So my questions are: Are these COP numbers not real? Are they in practice about 1 or less?
It appears to me that the technology isn't as efficient as I thought it was.

Do you have theories or facts that supports these claims?

Just good to know before I decide to install a heat pump.

A quote using google translate:
"Now an analysis from Statistics Norway (SSB) that heat pumps may not be as environmentally friendly as you thought. If one is to believe SSB, they contribute at least not to lower the overall power consumption.

Households with heat pump has in fact on average about the same power consumption as other households, it is going ahead SSB analyzes 2/2013."

Br.

Vidar
Let me get this clear. You use heat pumps as a heat source in Norway??!!! And these are used to heat your houses during winter? REALLY??!!

Zz.
 
  • #5
DrClaude
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Let me get this clear. You use heat pumps as a heat source in Norway??!!! And these are used to heat your houses during winter? REALLY??!!
Yes.
 
  • #6
jtbell
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You use heat pumps as a heat source in Norway??!!! And these are used to heat your houses during winter? REALLY??!!
This must be a different sort of heat pump from the ones people use in the USA, mainly in hot dry climates like Arizona, for cooling (instead of air conditioners)

heat pump (geothermal)
http://en.wikipedia.org/wiki/Geothermal_heat_pump

Yep, they're different in that they exchange heat with the ground instead the air.
 
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  • #7
ZapperZ
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This must be a different sort of heat pump from the ones people use in the USA, mainly in hot dry climates like Arizona, for cooling (instead of air conditioners)



http://en.wikipedia.org/wiki/Geothermal_heat_pump

Yep, they're different in that they exchange heat with the ground instead the air.
Based on what the OP wrote, and considering that it is being compared to a stove for heating, it appears that it is being used not for cooling (i.e. what a "heat pump" is usually used for), but rather for heating. Why else would someone compare this to a stove?

This is extremely inefficient, because most places that I know simply use fuel to heat either water or heat the air directly, rather than using a heat pump. That's why I'm a bit shocked at the implication (which I don't think is correct) that such a thing is used in Norway as a heat source.

Zz.
 
  • #8
sophiecentaur
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This must be a different sort of heat pump from the ones people use in the USA, mainly in hot dry climates like Arizona, for cooling (instead of air conditioners)
An air conditioner is a heat pump and many heat pumps can be connected / reconnected to provide heating or cooling. The effectiveness of any heat pump system will depend, ultimately, on the temperature difference between inside of your house. A nearby non-freezing river (or the sea) can a pretty good source but an area of ground with perma-frost will never be good value.
Any plans for using that form of heating should be based on the specific conditions of the location. The uninspiring statistics (alleged) in Norway may be the result of a lot of successful marketing of unsuitable systems. So someone may have managed to profit from the exercise. :biggrin:

A kWh of electricity will only be good value, however it's used, if the heat is conserved by good insulation. In Norway, it's a double whammy, I think. Thick socks and plenty of Gluhwein (or the equivalent) are called for.

I ask myself how long it will be economical to live comfortably in some of the places with extremes of temperature, as the price of energy increases. At least the boring old UK has a Goldilocks climate.
 
  • #9
DrClaude
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This is extremely inefficient, because most places that I know simply use fuel to heat either water or heat the air directly, rather than using a heat pump. That's why I'm a bit shocked at the implication (which I don't think is correct) that such a thing is used in Norway as a heat source.
It is used. I have one in my house, in northern Sweden.

Why do you say it is inefficient? Compared to direct heating of water using an electric water heater, you use much less electricity using a heat pump to heat up the water.
 
  • #10
ZapperZ
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It is used. I have one in my house, in northern Sweden.

Why do you say it is inefficient? Compared to direct heating of water using an electric water heater, you use much less electricity using a heat pump to heat up the water.
You need to look at the chain of 'events' from fuel to heat production.

In direct heating, fuel is used to directly heat either the water (radiators, etc.) or the air.

In your electric heat pump, fuel is used first to generate electricity, that is then used to run the heat engine, which in turn, generate the heat. You could have a 100% efficient heat engine (which isn't possible) and still lose quite a bit of efficiency at the electric turbine.

And thanks for the info that there are parts of the world using such a thing. I wasn't aware of that.

Zz.
 
  • #11
f95toli
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Yep, they're different in that they exchange heat with the ground instead the air.

Not all of them. Many people including my parents (my mum lives in the north of Sweden,and my dad in Norway) uses air heat pumps. It is certainly much cheaper (and more efficient) than using electrical radiators. which is usually the only other option (gas heating is very unusual in Norway and Sweden, oil is quite common).
Is should mention that both my parents also use wood burning stoves to help heat their houses up during cold days.

Heat pumps are also becoming popular here in the UK.
 
  • #12
DrClaude
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In your electric heat pump, fuel is used first to generate electricity
Not here. The electricity we have is mainly hydro.

We could have district heating, with hot water coming directly to the house, but the prices per kWh are basically the same as for electricity. Therefore, from the point of view of energy consumption alone, a heat pump has much lower running costs. But as I mentioned above, things get more complicated when you factor in the cost of the heat pump itself.
 
  • #13
DrClaude
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Not all of them. Many people including my parents (my mum lives in the north of Sweden,and my dad in Norway) uses air heat pumps. It is certainly much cheaper (and more efficient) than using electrical radiators.
Air source heat pumps are mostly (exclusively?) used here as auxiliary heating, because it does go below -18 °C sometimes :smile:
 
  • #14
sophiecentaur
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According to this wiki article, the COP (Coefficient of performance) of typical heat pumps, which is governed by the temperature difference, goes to about Unity with an outside temperature of -18C (0F). So it isn't surprising that Norway may not benefit (at least not all year round) from heat pump systems.

Installation and maintenance are significant issues but I am always amazed at how well actual refrigeration units tend to last, though. It seems to be always peripherals, like thermostats and door seals that let your average home fridge fail. Some 'bad' design there, I think. What happened to planned obsolescence?
 
  • #15
russ_watters
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1. If it cools, it is an air conditioner, not a heat pump. People just don't differentiate because all heat pumps have air conditioning modes, but not all air conditioners have heat pump modes.
2. If it uses water to dissipate/provide the heat, it is a water source air conditioner or heat pump.
3. Yes, heat pump COPs are for real. But the COP drops with a drop in the source temperature. So if you use an air source heat pump in a very cold climate, the COP may well be less than 1. Most won't allow you to run them in heat pump mode below a certain temperature though.
 
  • #16
ZapperZ
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Not here. The electricity we have is mainly hydro.
I guess that would make sense now, since if the idea is to reduce the use of hydrocarbons, then the use of electrical heat pumps, no matter how inefficient the "chain of events" are, will not use any hydrocarbons directly, when compared to the use of fuel for direct heating.

I had someone gave me a calculation of how inefficient it is in the conversion of fuel into electricity at a typical turbine. I think the number is like 15% or thereabouts. Do we know what is the energy conversion efficiency for a hydroelectric turbine?

Zz.
 
  • #17
russ_watters
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You need to look at the chain of 'events' from fuel to heat production.

In direct heating, fuel is used to directly heat either the water (radiators, etc.) or the air.

In your electric heat pump, fuel is used first to generate electricity, that is then used to run the heat engine, which in turn, generate the heat. You could have a 100% efficient heat engine (which isn't possible) and still lose quite a bit of efficiency at the electric turbine.

And thanks for the info that there are parts of the world using such a thing. I wasn't aware of that.

Zz.
1. Even if a natural gas power plant runs at only 40% efficiency and your heat pump only runs at a COP of 3, that's still 20% more heat from the heat pump than from direct gas firing.
2. People don't use heat pumps for overall cycle efficiency, they use them for cost. If you have an all-electric house with no access to natural gas, a heat pump saves you a ton of money over an electric resistance heater.
I had someone gave me a calculation of how inefficient it is in the conversion of fuel into electricity at a typical turbine. I think the number is like 15% or thereabouts.
Not even nuclear power is that low. A typical natural gas combined-cycle plant is 55-60%.
http://en.wikipedia.org/wiki/Combined_cycle#Efficiency_of_CCGT_plants
Do we know what is the energy conversion efficiency for a hydroelectric turbine?
Somewhere around 85% IIRC.
 
  • #18
Nugatory
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3. Yes, heat pump COPs are for real. But the COP drops with a drop in the source temperature. So if you use an air source heat pump in a very cold climate, the COP may well be less than 1. Most won't allow you to run them in heat pump mode below a certain temperature though.
Most residential heat pumps installed in North America use the outside air as the heat source/sink, so as you say won't heat effectively or efficiently below a given outside temperature, usually on the order of 0-10 degrees Celsius. This makes them very effective in the southern US where the winters are mild but so not mild that you can live completely without heat, auxiliary resistance heating seldom kicks in, and summer cooling is essential.

In the rest of the world, you often see installations in which the outside heat exchanger is a set of buried pipes, taking advantage of the near-constant year-round temperature of the ground below the frost line. These can be very efficient even in very cold climates; the catch is that they have appreciably higher initial installation costs which somewhat offsets the operational savings.
 
  • #19
phyzguy
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Let me get this clear. You use heat pumps as a heat source in Norway??!!! And these are used to heat your houses during winter? REALLY??!!Zz.
This is not so unusual. I had a air-source heat pump for heating the house in the winter when I lived in suburban Seattle. It functioned as an air conditioner in the summer and as a heat source in the winter, not that you need air conditioning very often in Seattle. To be clear, it had back up electrical heating coils that kicked in if the temperature got so low that the heat pump couldn't produce enough heat, but this rarely happened. One other thing that limited the efficiency in my system was that if it was cold and humid (which is often the case in Seattle), then the outside coils would ice up, and the system would run backwards, pumping heat out of the house into the coils, until the ice had melted.
 
  • #20
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as Sophie already said and I could agree a heat pump for heating your house in winter while it's very cold outside may not be that effective as for lower temperature regions were winters are less cold , Now in Norway depending on the region you can go as low as -30, maybe more sometimes , so thats some serious temperature to deal with.

But as we know the efficiency and the potential savings depend on the temperature difference between the two sides of the pump so I would say in a cold winter climate you would have to bury your pipes deep under ground where the earth gets warmer , I don't know how deep that is probably very deep, and not practical but in theory it would work kinda good.
 
  • #21
DrClaude
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Here are some typical numbers for a geothermal installation in Sweden. If you make one borehole straight down, it will be 100-200 m deep. You can also bury pipes some 0.6-1.5 m under ground level and lay a looping pipe, covering some 400-600 m2.
 
  • #22
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I had someone gave me a calculation of how inefficient it is in the conversion of fuel into electricity at a typical turbine. I think the number is like 15% or thereabouts. Do we know what is the energy conversion efficiency for a hydroelectric turbine?
I nearly spat my tea out when I read 15%, with aero-engines it's hard to design something worse than 60%. I guess the electricity generation comes with its own losses, but I think it should be no lower than 50% in the new combined cycle generation of gas power plants.
 
  • #23
Low-Q
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I guess that would make sense now, since if the idea is to reduce the use of hydrocarbons, then the use of electrical heat pumps, no matter how inefficient the "chain of events" are, will not use any hydrocarbons directly, when compared to the use of fuel for direct heating.

I had someone gave me a calculation of how inefficient it is in the conversion of fuel into electricity at a typical turbine. I think the number is like 15% or thereabouts. Do we know what is the energy conversion efficiency for a hydroelectric turbine?

Zz.
That is hard to say. The efficiency of a hydroplant is somewhat limited to the efficiency of the generators, which ends up around 80% - 90% output versus harnessed energy from the waterfall. Harnessed energy depends on how much water we allow to bypass through valves or between the turbine blades. Efficiency compared to the total kinetic energy of all the water in the river / waterfall might be rather low. But that isn't interesting as the water flow itself is done for free by nature.

Vidar
 
  • #24
Low-Q
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as Sophie already said and I could agree a heat pump for heating your house in winter while it's very cold outside may not be that effective as for lower temperature regions were winters are less cold , Now in Norway depending on the region you can go as low as -30, maybe more sometimes , so thats some serious temperature to deal with.

But as we know the efficiency and the potential savings depend on the temperature difference between the two sides of the pump so I would say in a cold winter climate you would have to bury your pipes deep under ground where the earth gets warmer , I don't know how deep that is probably very deep, and not practical but in theory it would work kinda good.
It is not very common for housholds to dig deep in the ground for these pipes. However, I see that some people spend some extra money in making a "ditch" around the house they're building, for laying pipes for their pump before the pipes are burried. It does not have to be very deep if the pipes covers a large area. Some people also drill holes several hundred meter into the rock. Very expensive though.

Vidar
 
  • #25
CWatters
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A correctly specified, designed and installed heat pump will definitely be cheaper to run than a standard electric heater. However if the specifier/installer does a bad job it's easy for a heat pump to perform badly.

Many early heat pumps had limited maximum power output. Worse still the maximum power output of an ASHP falls when the outside air temperature is cold - exactly the time when you need the most power. Most heat pumps are supplied with booster coils (COP=1) to provide the extra power needed when it's very cold. Normally the booster coil should only kick in when it's very cold but if the unit is undersize for the house then it kicks in too early and too frequently with massively increased bills.

The COP of the heat pump is also proportional to the temperature uplift. This means that they perform better when coupled to low temperature UFH or oversize radiators designed to operate at lower temperatures. Some installers have been replacing gas fired boilers with ASHP without changing the radiators.

This is also an issue for Domestic Hot Water which if stored in a tank needs to be >60C to prevent Legionnaires' disease. If the household needs a lot of DHW then that also reduces the average COP.

So to get the best out of a heat pump make sure the heat pump is correctly sized for the house. Big houses might need two! Make sure your house is well insulated so that it's rare for the booster to kick in. Couple it to a low temperature heating system. Minimise the amount of DHW needed.

I believe many of the bad/negative reviews are as a result of getting the design or installation wrong. Sometimes an installer should tell the owner they would be better to use mains gas.
 

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