Use waste heat to drive air-conditioning 1

[petermeachem]

It's been a while ! since I did thermodynamics but I think it would be possible to use waste heat to drive a domestic air-conditioner.

The scenario is that we are thinking of buying a house in Portugal which has no electricity. I have discovered that it is possible to buy a generator based on a Stirling cycle engine. Unfortunately, this produces more heat than electricity, which is about the last thing you need in Portugal.

Hope someone can help a refugee from tek-tips.

 

[chicopee]

Isn't the stirling cycle more efficient than an open-air cycle which closely approximates gasoline engines. Also, would it not be better to use a diesel cycle to drive the generator? After all diesel engine are more prevalent than stirling cycle engines.
Waste heat could used for an absorption air conditioner. I know of several institutions that use aborption air conditioning systems and the heat needed is generated from power boilers At one time, certain brands of refrigerators were actually absorption system and the fuel needed to generate heat was natural gas piped into the refrigerator. These refrigerators can still be found but are becoming rare. This type of refrigerator lasted for decades with virtually no maintemance.
Waste heat could also be used with heat pumps as home heating systems. Heat pumps use the same refrigeration cycle and will use the heat of compression to heat structures. It is an efficient heating system but can be expensive when repairs are needed to the compressor.

 

[petermeachem]

I don't really want a diesel engine banging away near my house thanks. Stirling engines are quiet and low maintenance. I read this evening about a sealed free piston Stirling that generated electricity with a linear alternator.
I had forgotten about gas fridges. I shall investigate.
Thanks.

 

[quark]

Absorption machines generally produce refrigeration effect by heat intake. But they are not totally electricity free. You require electricity to drive refrigerant and absorbant pumps. Smaller models are much costlier when compared to conventional vapor compression systems.

Sometime back there was thread asking the explanation for a solar refrigerator. (It was patented by a South African student, but I couldn't get the link which explains the theory fully) Check that and it may help you.

 

[davefitz]

The latest thing in Asia is the use of the Capstone microturbine with an absorption air conditioner on the back end. In Portugal, improved turbine output and efficiency can be had by incuding an inlet air chiller to the compressor. I believe the system is marketd in Europe- see issue of "Modern Power Systems " circa 2001-2002 for similar articles.

The Capstone unit starts at about $40K USD ( 35 KWe)plus cost of gas compressor plus absorption unit, if I remember right.

 

[petermeachem]

That's a bit steep for domestic, about the same as the cost of the house.
I found this huge list

http://archive.greenpeace.org/gopher/campaigns/air/1993/ozhold3.txt

This is US based only and I haven't actually read it all as yet.
A small amount of electricity is fairly easy to produce. The problem is you get too much heat with it which is wasteful. As far as I can see, fuel cells are better but I think a little expensive yet.

 

[chicopee]

Large absorption systems have circulating pumps but smaller ones normally dont have them.
Yeah pretty expensive stuff for residential application!!

 

[boilerdoc]

Hi Petermeachem,
if you think that the capstone microturbine mentioned by davefitz is too expensive for domestic use, better stop investigating in stirling cycle systems unless you are able to tinker your own machine. Stirling engines make sense when your fuel is really cheap like wood, other biomass or waste heat from existing combustion processes.Also the cost for an absorption chiller for your residence (unless you bought a palace), compared in Euro per m2 floor space will drive tears in your eyes. I would install a photovoltaic system for electricity and leave the windows open for airconditioning, its not that hot in Portugal.

 

[davefitz]

another HVAC idea recently utilized is to use a parabolic solar collector to heat brine or oil, and use that to drive the absorption unit. Yazaki sells 10 Ton units at a low price. Only electricity usedis to drive circ pumps.

A larger scale up of this was used recently to chill the inlet air of a large Utility frame Gas turbine installed in Arizona, USA

 

[petermeachem]

Setra look at

http://www.microgen.com/products1.html

There is nothing to tinker with on a Stirling. Also

http://www.bg-group.com/news/archive_2002/080102-pr.htm

and

http://www.onboardenergy.com/victron_energy.htm

Solar looks good too. But I would like to use waste heat and we do need reliable electricity. I think we are a bit cutting edge here.

I don't know where you live Setra, but from a UK perspective, I can assure you that Portugal is hot.

 

[poetix99]

It's a dry heat.

 

[boilerdoc]

petermeachem,
you did not mention what source your waste heat is coming from. The stirling works on external combustion processes. Unless there is any industrial or commercial activity around producing waste heat you have to burn some kind of fuel to drive your stirling engine.

 

[petermeachem]

It's going to have to bottled gas I'm afraid. That seems to be the easiest fuel to obtain. There isn't any activity of any sort where we are thinking of. I'm looking into such things as liquified biomass, but it has to be pretty automatic system.

 

[boilerdoc]

So you think about buying bottled Gas and burn it to drive a stirling engine with generator and use the combustion gas to power an adsorption chiller for AC purpose?
For your generator unit with around 5 kW electrical capacity we talk about Euro 15.00,- to 20.000,- investment.
These units are available, but without long term experience about service life.
The adsorbtion chiller in this capacity range will cost you another Euro 10.000,- plus the cost of Gas supply.
The overall efficiency will be very poor because you can never consume the full capacity of your generator and your chiller at the same time over the day.
I make my living with consultancy in renewable energy, and I appreciate your enthusiasm, but you should really focus on solar power for your electricity needs.

 

[petermeachem]

I'm sure you know what you are talking about, but I read that the price was supposed to be comparable with a combi boiler, which is a lot less than you are saying.
How can we store solar generated electricity? For when the sun goes down.