Friday, February 15, 2008

Heat Pumps

One of the agonies of home ownership is having to get your home heating and air conditioning systems overhauled, and sometimes replaced. In Texas AC compressors last some five to ten years. Most Texas homes use natural gas furnaces, and they are often of mediocre performance. In addition natural gas is also used to hear water, and for cooking. The long term supply of natural gas is uncertain, but significant untapped reserves cannot be ruled out. In addition enormous supplies of Natural Gas are avaliable from the Persian Gulf. There are economic reasons for prefering local energy sources to natural gas.

Burning natural gas creates greenhouse gases. This is the most significant issue with gas, and needs to be considered quite appart from other issues. The principle for energy use should be to replace carbon source energy where and when it is possible, and to make its use as efficient as possible, in situations where it cannot be replaced. Electricity and sunlight can efficiently replace natural gas. Since electricity can be generated by non carbon sources, using electricity in place of natural gas is moving toward non-carbon sourcing.

In an earlier post I pointed to the advantages of solar water heating, In most localities, solar water heaters pay for themselves over time. This appears to ne the case even in Toronto. Solar water heating can reduce household carbon footprints by 20%, and solar water heaters should be manditory for new homes.

Gas ranges can be replaced by electric ranges. Home construction standards should specify electrical stoves in all new homes.

Finally, we have the issue of heating. As I pointed out almost all homes have to air temprature control systems, a furnace for winter heat, and an air conditioner to control summer heat. Now the interesting thing about air conditioning is that their cooling cycle can be reversed. An air conditioner is basically a pumping system that moves heat around. Basically the air conditioner collects heat from inside the home, and moves it outside. The process can be reversed. It is possible to collect heat from the outside and move it inside. That is what an heat pump comes in. A heat pump is basically a reversible air conditioner that moves some heat from outside a structure to inside. But how can you get heat from cold winter air? basically by chilling it even more. Just as air conditioners are able to deliver chilled air inside during the summer, while generating hot air outside, heat pumps generate even colder winter air outside, while delivering warm air indoors. Heat pumps can deliver warm heat indoors even in sub-zero Canadian winter weather. They can also keep Texans cool during hotter than hell Texas Summer days.

There are three basic types of heat pumps, but only two of them are typically installed. The first is air-source heat pump. This is your basic air conditioner with a redesign that allows it to move hot air inside during the winter. Some of these models can be as much as 5 times more efficient as traditional electric heaters, and they are also very efficient air conditioners.

The second type of heat pump is called a geo coupled heat pump. Fluid from the system is circulated through tubing under ground. Heat is dumped into the ground in the summer, and returned to the house during the winter. Geo-coupled systems are actually more efficient than air-source systems, but they are also more expensive. In addition, the placement of significant parts of the system underground can create significant headaches, if the system needs repair. Geo-coupled systems also require more yard space since heat cannot be dispersed into a small area. Geo-coupled heat pump systems are also efficient for heating water.

Geo-coupled heat pump systems work well with commercial and industrial buildings. The underground system can, for example be placed under parking lots.

Water source heat pumps move heat back and forth from water. They are far less common and probably will continue to be.

Electrical utilities have reasons for wanting to see their customers install heat pumps instead of gas furnaces. Heat pumps increase winter electrical use. This means that generators solely devoted to summer peak power have winter uses as well. At present electrical companies use gas turbine generators to produce peak electricity. Gas is an expensive fuel for electrical generation, but the turbing generators are cheap. There are three principle drawbacks to the system. First it produces greenhouse gas. Secondly the long term price trend for natural gas is toward increasing cost. Thirdly, it is not clear how long the gas supply will last. Thus electrical companies considering the inevitable replacement of natural gas generators, want to find year round uses for new generators.

Thus electrical companies have a motive to subsidize the purchase of heat pumps by their customers. Heat pumps promote more consistent year round electrical use patterns, thus reducing the expensive necessity of maintaining power plants solely for summer use. Geo-coupled heat pumps especially lower summer air conditioning related electrical use. The lower electrical demand translates lower peak power demands, hence fewer peak power plants need to be maintained. In this case efficiency works to create a better balanced electrical system.

It is clear then that new building codes should require air-source or geothermal heat pumps, or other carbon free heating and cooling options. Electrical companies have incentives to offer rebates to customers switching to heat pumps, with higher rebates going to home owners who install geo-coupled systems. Local, state and national governments should also subsidize conversion of existing homes to heat pumps. Natural gas can be taxed to provide money for the installation of heat pumps in the homes of poorer people. The the added expense of paying taxes provide an incentive for all homeowners to switch to low carbon heating, while the government program removes the replacement cost burden from the poor.

15 comments:

DV8 2XL said...

Heat pumps do work even here in Montreal, Quebec where the winters are normally colder than Toronto. However in almost all cases they must be backed up by an auxiliary source of heat to deal with cold snaps and for defrosting the coil in the ones that don't have ground-loops, (which is the majority of installations.)

Good friends of ours have a system fitted to their forced air electric furnace, and are pleased with it. I have asked what sort of savings they have realized and I have been told that it is unclear. It would seem that now that they enjoy air-conditioning during the summer any savings that they may have gotten in winter heating are used up by summer cooling.

Nevertheless, this type of geothermal energy should be exploited as much as possible, and I wholeheartedly agree that its use should be mandated by the Building Code.

Charles Barton said...

It would seem that now that they enjoy air-conditioning during the summer any savings that they may have gotten in winter heating are used up by summer cooling. - DV8 2XL

You have just sited an example of Jevon's Paradox. Improvements in energy efficiency lead to greater energy use. In Texas most people would probably go for air source heat pimps. That would not cut summer electrical demand that much, but the use of heat pumps in the winter would mean that less of the summer capacity would go to waste during the rest of the year.

randal.leavitt said...

Hmmmm ... there are lots of issues here. Essentially we want to put heat into our buildings when it is cold outside (i.e. work uphill) and move heat out of our buildings when it is warm outside (i.e. work uphill again). Putting the heat in seems easier to me - use an electric powered plasma torch. Getting the heat out is a bit more tricky - a heat pump that moves it somewhere else seems like the best alternative. I've read about devices that convert heat directly into electricity. This seems like the answer - take the heat from your house, move it to the basement where is can be concentrated, convert it to electricity, and run your computer with it. Otherwise we have the "heat garbage" problem that does not have a nice socially acceptable solution (i.e. you dont want me to dump my heat in your yard).

randal.leavitt said...

Hmmmm ... there are lots of issues here. Essentially we want to put heat into our buildings when it is cold outside (i.e. work uphill) and move heat out of our buildings when it is warm outside (i.e. work uphill again). Putting the heat in seems easier to me - use an electric powered plasma torch. Getting the heat out is a bit more tricky - a heat pump that moves it somewhere else seems like the best alternative. I've read about devices that convert heat directly into electricity. This seems like the answer - take the heat from your house, move it to the basement where is can be concentrated, convert it to electricity, and run your computer with it. Otherwise we have the "heat garbage" problem that does not have a nice socially acceptable solution (i.e. you dont want me to dump my heat in your yard).

Joffan said...

I'd like to make plea here for calling the ground-loop heat-pumps

--- geo-coupled ---

rather than geothermal. The system doesn't use ground heat as a source of energy; it uses the ground as a big heat exchange with (fairly) steady temperature to shuffle heat energy in and out. The process is driven by the pumps, not the ground. Reserving "geothermal" for those applications where the heat from the earth provides the energy for a process would bring a little more clarity to the muddled language in this area, particularly claims of "geothermal power" for these heat pumps.

Charles Barton said...

Joffan, I chose geothermal, because that appears to be the tern adopted by convention. You make the case for precision rather than convention. You are absolutely correct. But most people don't know the difference. When I google ground source heat pump, I bring up an article from the wikipedia titled "Geothermal exchange heat pump." What can I tell you? Precision looses to popular language, I am afraid.

Joffan said...

and yet you didn't use aerothermal or hydrothermal...

No. This confusion is deliberate on the part of those who would pretend there is more going on in the minority power sources than there really is. By all means use ground-source heat pump rather than geocoupled, but geothermal is plain wrong. "Popular usage" is less than a year old at most I'd say and is not yet a real excuse.

Charles Barton said...

Joffan, you might appreciate this,

For the world is a mountain
of shit : if it's going to
be moved at all, it's got
to be taken by handfuls.

From:The Terms in Which I Think of Reality
By Allen Ginsberg

DaveMart said...

Ground source heat pumps are pretty expensive, but fortunately the latest air pumps now work at temperatures well below zero, in the case of the new CO2 Eco-cute in Japan down to -15C:
http://www.r744.com/knowledge/faq/files/ecocute_all.pdf
Technology and Market Development of CO Heat Pump Water Heaters ...

It might be some time before they are available in the US, as they use water as is common in Japan and Europe and so could not be used for air-conditioning.

If you can't wait you could always buy the Canadian Hollowell, which is good for down to -30C
http://www.gotohallowell.com/technical.html
Hallowell International: Technical Data

They haven't sold nearly as many units as the Japanese though, so perhaps reliability might be more of a concern.

Charles Barton said...

Davemart, Tyler Hamilton recently did a story on Hollowell.
http://tyler.blogware.com/blog/_archives/2008/2/11/3517787.html

Hollowell is actually an American company, but they do a lot of business in Canada. What I have read suggest that there may be a downside to having a heat pump that provides heating at - 30 C.

Hamilton writes that the Hallowell "system is three times more efficient than resistance heating." I believe that more efficient heat pumps can achieve twice that, but peter out at producing heat at around - 15 to - 18 C.

Brad F said...

I'm with Joffan on the nomenclature. Ground source more accurately describes the operation of a heat pump and, in fact, is how the industry has described itsef for over 20 years.

When I hear the word geothermal, I think hot springs and steam. I recently read a post somewhere in which the author, while advocating the use of GSHPs, declared that geothermal energy was free! As if the electricity to run the system was inconsequential. To me, the author seemed both ignorant of how the system worked, and was confusing hot springs/hot rocks with a heat pump system.

The more people eschew the term geothermal, the clearer the concepts will become (I hope).

Regarding efficiency, in the heating mode a Coefficient of Performance of 3 (also called 300% efficiency) is about the bottom for a properly designed GSHP system. But I'd like to know where you can find a seasonal CoP of 6, Charles. I've seen high CoPs claimed, but only under optimum conditions (generally a relatively high source temperature). It is the seasonal efficiency that matters.

I'm very interested in Hallowell's approach to a cold climate heat pump. Although I've been longing for a GSHP for years, an air source system with a similar CoP might be a better option for me, especially after paying to put a new lawn down last year.

Charles Barton said...

Hay guys, I already chaqnged it to Geo-source, even though I think that name may be a loosing cause.

Heat Pumps Medford said...

Thanks for that, a lot of people are understandably hesitant to get heat pumps because they don't understand it and they don't know if it works as well. this article shows that they do!

Alexander said...

Good post very interesting

heat pump ratings said...

A heat pump is a machine or device that diverts heat from one location at a lower temperature to another location. A heat pump can be used to provide heating or cooling. Even though the heat pump can heat, it still uses the same basic refrigeration cycle to do this. Heat pumps have the ability to move heat energy from one environment to another, and in either direction

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