Energy Matters Forums

[solar?]

Hi,

I currently have an off peak electric hot water, and no house heating/cooling to speak of. I looked around the internet, and rather liked the idea of solar thermal air conditioning. I understand that ice was made form heat back in 1878, and gas powered fridges are still around, but there only seem to be commercially sized systems available. I hoped that there was a system that could use excess heat during summer to make it cooler inside.

Please can I have some suggestions re systems for HWS and heating/cooling? Also I was thinking that a heat pump for HWS is similar to a heat pump for a heating/cooling split system, maybe there is a combined system, hoping that would mean less items to operate.

My place needs some work, new bathroom in particular, can't use the shower as it leaks, luckily I like baths, and I was hoping to get work for that and other things done in one hit.

Looking around the site, many of you know way more than I, and I would appreciate any suggestions.

Cheers

[Tracker]

I hoped that there was a system that could use excess heat during summer to make it cooler inside.

I think that we would ALL like to know of such a system... I might be a little simple, but I would suggest that IF there was an efficient technology to do it, then it WOULD exist right now..

I presume that you are talking about the camping fridges etc. that use the Absorption process and ammonia (I think) as the refrigerant..
It is a wonder that you can't use an Evac-Tube Solar Collector to achieve the same process..
Does anyone know the thermo-reason, why it is not done..?

It could have something to do with the quantity of AMMONIA that would be needed and the inherent danger of such a substance in someone's roof..

PS - http://scusolar.org/technology.thermal
If you.. ECOSIA.org .. Absorption Chiller, you will actually find reference to the technology.. I can't help the feeling that it is FAR from being compact technology..
..
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[Gordon-Loomberah]

Please can I have some suggestions re systems for HWS and heating/cooling?

I use a system comprised of 78 evacuated tubes for hydronic heating of the house and a 30 tube system for the hot water. I have no electric or gas boosting. There are generally only 2 of us in the house, but it has mostly been overcast with showers and almost no sun at all for the past week and a half, and heavy overcast with continuous rain today, yet we still have hot water I manage this by means of a heat exchanger which enables me to use heat from the hydronics hot water to heat the hot (or luke warm as it now is) water for the shower.

For cooling, I'm planning to use a couple of very efficient reverse cycle air conditioners. Being off-grid, they have to be very efficient, to get the most cooling possible from the limited amount of available power.
I am thinking of adding a bit of heat from the hydronics water to the input of the ACs on sunny days in winter to maximise the amount of heating available from the hot water.

[Tracker]

For cooling, I'm planning to use a couple of very efficient reverse cycle air conditioners. ...

Gordon, have you actually found anything that is a standout winner in the efficiency stakes..

I have had it suggested to me that it's better to use a smaller device run at MAX, rather than larger units that (INVERTER) change speeds to reduce output..

Have you ever encountered an absorption cooling system suitable for domestic operation??
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[Gordon-Loomberah]

The Mitsubishi 2.5 kW MSZ-FB25VA with EER and COP (cool & heat) of nearly 5, seem as good as there is, and they are apparently more reliable than some others with similar COPs.

From my reading of various comparison documents, it seems that smaller units are more efficient whether or not they are run at full power, which is why I went for 2 * 2.5kW units rather than a single 5kW. It gives more flexibility regarding the areas I might want to cool as well.

I've looked around online a bit over the years for suitable absorption type cooling gear, but haven't found anything really useful. I suspect it would be a matter of sitting down with a refrigeration engineer and working out something. I doubt it would end up being very compact, and it is sure to be quite an expensive project too.
However, I see no reason why a scaled up kerosene or gas refrigeration unit with concentrated solar for the energy source, and a fan to circulate the cold air would not work. Certainly the typical gas fridge isn't a continuous cycle unit, but dual units would overcome that, and there may well be continuous cycle designs around now anyway.

[solar?]

Thankyou for your responses. Please what is a COP? Through the internet I did find a man in Queensland who is installing absorption chilling systems on a commercial scale. Lithium bromide seems to be the product used, rather than ammonia. CSIRO Newcastle has been set the goal of coming up with a residential system as air conditioning looks likely to continue to require more power in cities.

I was intrigued by the evacuated tube for HWS and hydronic heating. I live in Melbourne so hopefully it would still be viable. Please could the heat exchanger option you mentioned be explained.

Cheers.

[Tracker]

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COP - Coefficient of Performance..
http://en.wikipedia.org/wiki/Heat_pump

I think it used to be know as COE - Coefficient of Efficiency - and as this name implies, it's the POWER GAIN from using heat-pump technology.. eg.. I use a device with a COP of 5 and using 1Kw input power, I can generate 5Kw of Heat or Cold, when compared to resistive heating..
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[Gordon-Loomberah]

I was intrigued by the evacuated tube for HWS and hydronic heating. I live in Melbourne so hopefully it would still be viable. Please could the heat exchanger option you mentioned be explained.

Yes, it should work ok in Melbourne if you have a well exposed position for evacuated tubes, enough of them for the job, and tilted up for winter sun.

The hydronics tank is heated via 78 evac. tubes (a search of the forums will show a photo of the tubes and tanks behind the house) and is an open tank system, ie not pressurised, and it will one day also be connected to a wetback stove. The 30 evac. tube hot water system is pressurised (250kPa), and both are connected to independent circuits via an inlet and outlet on the heat exchanger. The hydronics side is in parallel with the hydronics heater units circuit in the house, and the hot water is between hot water system and the outlets in the house. The heat exchanger has a very large internal surface area of plates between the hydronics and hot water circuits and is able to transfer many kW of heat in quite a small unit, about the size of a car's internal heater radiator. If the hot water isnt quite warm enough for a shower, I just run the hydronics pump to circulate hot water through the heat exchanger. I also run it when using the dishwasher or washing machine to increase the hot water temperature if needed, to avoid/reduce the operation of the internal ~2400W heaters. We've just had yet another day of overcast and rain showers , but the water, using the hydronics, is still plenty hot enough for a shower

[solar?]

Most informative.

I am curious as to the reasons behind having evacuated tubes in a pressurised and unpressurised system. Please could you let me know why the choice for the hydronic and HWS to be different?

[Gordon-Loomberah]

Pressurised hot water, because I like the water to come out of the shower head at speed, rather than a dribble It is fed from the same tank as the cold water for the house @250kPa, so no messing around with HP cold and LP hot balance- differing pressure makes it more difficult to get the temperature correct.

I live purely on rainwater I collect from the roof here, and pump it up to a tank to supply a constant 250kPa to the house when I have sufficient solar power, and a full tank (5000l) will last for a couple of weeks if I'm not irrigating the vegie garden.

For the hydronics the plan is to plumb in the wood fired stove. Wetback stoves must always be connected to an open vented tank, they have the ability to easily boil a lot of water. Exploding hot water tanks... well, have you seen the Mythbusters episode where they explode one by removing the thermostat and continue heating the water? You dont want that happening anywhere nearby!