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Author Topic: Could you use central heating radiators and pipes to COOL your house in summer?  (Read 41204 times)

Offline Bored chemist

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"I know, I was hoping that convention could work the other way to; the only problem is hot air rises and cold air falls."

Convection will run in reverse. The cold air runs down the radiator and onto the floor wher it cools the rest of the room. Meanwhile warm air is drawn down  to the cold radiator.


"If the water was flowing through the system there would obviously be a section that had cooled the water down in the first place, so it would be re-cooled on passing through it."

I know it would have to be cooled if you were going to recirculate it. What I asked was how you would do that (specifically I said "how do you cool it back down again".

"I think it would be silly to have a freezing cold radiator, you can just see the headline 'little child gets tongue suck'. Not forgetting that, frozen water will not flow. "

Well, that's why I listed that as a potential problem.



One idea that strikes me is that you could use a swamp cooler type arrangement outside to cool a radiator to supply the cold water to circulate through the house radiators.
That gets round the problem that swamp coolers humidify the air- it doesn't matter so much if the air they are humidifying is outside.
It also means that the water can't get colder than the dew point of the air so there won't be a condensation problem.

 

sooyeah

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"I know, I was hoping that convention could work the other way to; the only problem is hot air rises and cold air falls."

Convection will run in reverse. The cold air runs down the radiator and onto the floor wher it cools the rest of the room. Meanwhile warm air is drawn down  to the cold radiator.

Yes, you bring the hot air to the cold radiator, that way the air will gradually get colder. It compensating for the reverse Convection.

"If the water was flowing through the system there would obviously be a section that had cooled the water down in the first place, so it would be re-cooled on passing through it."

I know it would have to be cooled if you were going to recirculate it. What I asked was how you would do that (specifically I said "how do you cool it back down again".

Well there are lots of ways to cool water, you could use the heat pump system. I just think which ever way you did do it should use as little electricity as possible, and not dump the heat out side, as air con does.
 
"I think it would be silly to have a freezing cold radiator, you can just see the headline 'little child gets tongue suck'. Not forgetting that, frozen water will not flow. "

Well, that's why I listed that as a potential problem.

One idea that strikes me is that you could use a swamp cooler type arrangement outside to cool a radiator to supply the cold water to circulate through the house radiators.
That gets round the problem that swamp coolers humidify the air- it doesn't matter so much if the air they are humidifying is outside.
It also means that the water can't get colder than the dew point of the air so there won't be a condensation problem.

Except you would need one on every radiator. Or are you thinking that you could have one big-one at a certain point in the chain and that would cool the water down for the whole system? That would expose the water and you would get evaporation and therefore need to top up the water supply consistently.
Overall that would make the system more complex and use more energy surely?

Also condensation has a benefit as you remove water from the air. So I'm thinking that you would just need to design some form of cover to stop people touching it.
 

Offline techmind

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I would like to know if it would be possible to run Cold water through your central heating system?

Doing so would cool the air around the radiator.
If you connected a fan/vent system to either move the hot air from above to the radiator or just found a way to move the air around the room; the effect should work to reduce the overall temperature in the room.
When you complete the picture, what you are describing basically IS an air conditioning system...

In addition to what you've mentioned, you also need a system to cool the water down, as it will otherwise soon reach the temperature of the rooms. So you need a "refridgeration" module. This is a heat pump which pumps the heat-energy out of the water and dumps it into the air outside, the ground, or a convenient pond/lake or something.

As far as I can make out, the installed air-con system at my workplace pumps cooled water around the building. The ceiling-mounted cooling units are special "radiators" but with lots of thin fins to help the heat transfer despite a fairly modest temperature difference between the fins and the air. There's also a fan to circulate the air through the fins of the "radiator" because convection is not really strong enough because the temperature-difference is too small. There's some kind of system to catch the drips of condensation and a pipe to drain them away. Then outside the back of the building is a bank of refridgeration/heat-pump units to cool the water.

Unfortunately there's a very simple theoretical limit on the efficiency of any heat-pump, and for refridgeration device the efficiency rapidly gets worse as the difference increases between the temperature you're trying to cool to and the temperature at which you can dump/sink the heat. Although you might save some infrastructure by re-using existing heating radiator systems, overall the running costs can't be any lower than a dedicated cooling system... and since existing radiators aren't optimised for cooling it'll probably be much less effective and efficient overall. Sorry.

To minimise condensation (which is going to cost a lot of energy but not achieve much cooling) I imagine you'd want to run the water ("radiators") not too much below the target air temperature. This implies that you're going to need forced airflow (fans) to assist the air-circulation around the cold-"radiator" fins.
« Last Edit: 04/10/2007 01:01:21 by techmind »
 

lyner

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But any system you use for shifting heat away will cost energy / money. The transport method - cold air or cold water  is not really relevant, except to the installer. Unless you live next to the sea or a river, you need a heat pump.
 

sooyeah

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Unfortunately there's a very simple theoretical limit on the efficiency of any heat-pump, and for refridgeration device the efficiency rapidly gets worse as the difference increases between the temperature you're trying to cool to and the temperature at which you can dump/sink the heat. Although you might save some infrastructure by re-using existing heating radiator systems, overall the running costs can't be any lower than a dedicated cooling system...

That is debatable. This system could produce an exceptable temperature reduction, using less energy, and removing moisture at the same time.
If you used the heat pump method for the heating and cooling of the water, then you would surely have a greater reduction on the energy used. Heat pumps are recommended because they use less energy; they store the heat and cold and then tap into that save resource as needed.

and since existing radiators aren't optimised for cooling it'll probably be much less effective and efficient overall. Sorry.

I know they are not, that is why you would need a fan system to aid the air flow around the room.

To minimise condensation (which is going to cost a lot of energy but not achieve much cooling)

Is that correct? Condensation will occur naturally and has a benefit of removing moisture from the air(currently a job preformed by a dehumidifier) this system if designed properly could combine central heating, air-conditioning, a dehumidifier and use the heat pump system to heat and cool the water.
It would hopefully be a low energy all-round system.

As you already said you would need less materials to install it, and all the others could be replaced by it, that makes it a far greener system.
You design it to be a low energy system. The only part of the heat pump system you would use would be the heat and cold storage hopefully the main system could work the same as it does today.   

I imagine you'd want to run the water ("radiators") not too much below the target air temperature. This implies that you're going to need forced airflow (fans) to assist the air-circulation around the cold-"radiator" fins.

A small solar powered fan, combined with a funnel could easily do that. However, you may not envision this system as I do, but I don't see any necessity to use electricity from the main grid to run the fans. That again would reduce the energy burden of running the system itself.

I'm actually thinking that you would bring the hot air to the radiator, to below the radiator, it would then naturally rise and cool as it did so.

Thankfully hot and cold water act differently and have different affects on the materals they pass over, valves could be designed to shut and open from the temperature of the water inside the system.
Solar powered fans could be designed to come on only when the temperature of the radiator reached a certain level.
The condensed water could be drained and then stored in a tank, then used as a means to refill the system should it become low, which would reduce the systems overall use of water from the water company.
All these things could be combined to have a low energy system.

I post it for all, it belongs to the people. The Government can pattern it. ;D I'm sure some science student reading this has already figured out how to work it. Go nuts!!!  :)
 
« Last Edit: 07/10/2007 01:07:10 by sooyeah »
 

lyner

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But where is the source of energy to keep the circulating water cool? (Assuming you have no source of already-cooled water). You cannot ignore this  problem.
I was not aware that there is any debate that a heat pump requires more energy input the bigger the target change in temperature. Some basic thermodynamics here, I'm afraid.

Instead of a solar powered electric fan  you could  do what is done in many desert countries - that is to have a central well in a building which acts like a chimney and produces natural circulation (convection) of air, driven by the Sun. Water at the bottom of the column can be evaporated and produce cooling. This is no good in humid areas, though.
 

Offline Atomic-S

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I would like to add some insights from Arizona. There are ways of cooling very efficiently if the humidity is not too high. First I will repeat what was said above about the cooling tower effect. That is used here in Arizona to cool outdoor bus stops. Over the structure is a "chimney" containing some kind of filter pads and a pump and a water tank. The pump wets the pads, the pads add moisture to the air, cooling and causing it to condense. The air then falls, causing a light breeze upon the people below. This is not dramatic cooling, but enough to make a difference. The same effect is used in this building where I am: an evaporative "swamp" cooler is on the roof. When the weather requires only a little cooling, the windows are opened up, the machine's pump is turned on but rhe fan left off. The convection caused by the cooler and therefore denser air in the machine draws air downward through it, creating a soft flow of cooled and moister water through the building. The electricity required to run it in this mode is only what is required for a small pump.

Another insight:  The power plant that is or was located here in the city has a section where there are huge fans blowing through some kind of a box. I believe that this is the cooling tower, and I think it basically works as follows:  Hot water from the turbines is sprayed through some kind of filter, air blows, causing part to evaporate and the rest to be cooled substantially, and the cooled water is then returned to the machinery.

Now when it comes to making a really low-electricity-use cooling system, both of these ideas are useful. Dispensing entirely with the radiators, you could have a filter box on the building roof, with the water and pump, and just have that flowing and by convection the wetter air would come down into the building, cooling it. (Windows must be open below).  The pump could e vne be run by solar panels or even a wind turbine. But keep in mind that this may be inadequate if the weather becomes unfavorable in terms of too hot, too humid, or too windy. To turn then to your radiator idea, I think the cheapest way you could supply cooled water to the radiators would be having a unit outside in which the warmer water exiting the radiators would flow into nozzles at the top of a box, then rain down into a collecting area in the bottom, and from thence be recirculated into the radiators again. During its descent, the water droplets would cool by evaporation. Therefore there would be some water loss, which would have to be made up from the city water mains or some source, but this would not be a great cost in most areas.  A fan in the evaprator box might make the process more efficient, but also might be unnecessary if the box were quite tall and there were some light natural breezes.  Because the temperature drop of the water would be modest, the radiators inside would have to have, as has been mentioned, additonal fans to force air through them. I do not know if this system would get cold enough to cause condensation inside; I rather doubt it because the water itself is being cooled by evaporation, so it would not go below the outdoor dew point. Noneetheless, there would be some cooling. This system would be extraordinarily inexpensive to operate, basically you might need no more power than for the water pump and a few small fans. But of course will not produce the cooling power of a more expensive and power guzzling refrigeration system. For this reason, such a cooling system should be accompanied by careful attention to the condition of the building, such as whether the insulation is adequate, the roof painted white, ventilation in the attic or overhead space, trees to shade the structure from the direct sun, etc.
 

lyner

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Very nice - if you have the right levels of humidity.
In the UK you have to work much harder, nearly every day, to remove heat - it's so sweaty most of the time. It costs you.
 

Offline Atomic-S

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In your climate, the big challenge is not so much cooling as dehumidifying. Thus, a significant correllary question to the original one, is, what are the options for dehumidifying cheaply using existing radiators (or perhaps some other means)? Standard refrigeration can do it but that is costly to install and costly to operate.
 

lyner

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The latent heat of vaporisation  is always going to be the bottom line. There can be  several kg of water to get rid of  from a house full of humid air. That is going to cost a fair bit to remove, however you choose to do it. Air conditioners are not, now, a silly price and achieve the effect more conveniently than ice cold  room radiators. In any case, you would need to have a drainage system to deal with the condensate on the radiators - costly and intrusive. Circulating dried air is much easier.
People should try to get used to humidity - it is very costly ,in carbon, to deal with it.
 

Offline Atomic-S

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Unless someone can figure a way to do it with the sun -- by the way, what kind of sunshine do you get there in the UK during that time of year?
 

lyner

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A solar powered refrigeration system is not beyond the bounds of possibility.
 

Offline Atomic-S

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True, but is there any way to do it at reasonable cost?
 

lyner

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An 'absorption' type unit could shift a few hundred watts worth of heat. A 2m reflector, focused on the right part would provide enough power when the Sun was shining. That's when it would be most useful, too. They are not efficient but, with no  moving parts, they last for ever (?) when undisturbed. I had a tiny one in my VW camper and it kept drinks cool. The beauty was that it ran on mains, 12V and camping gaz, silently.
Hardly suitable for keeping a whole house cool, though and useless on long hot nights.
 

Offline Nobody's Confidant

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Well, if you turned off the radiators, there would be an absence of heat. And absence of heat is cold. So yes, technically speaking, using radiators(or rather, NOT using radiators) could cool the house.
 

sooyeah

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Well, if you turned off the radiators, there would be an absence of heat. And absence of heat is cold. So yes, technically speaking, using radiators(or rather, NOT using radiators) could cool the house.

You are missing the point, the idea was to pump cold water (very cold water) through the central heating system, to make the radiators colder, and by doing so to cool the room more and maybe remove some moisture too. 
 

lyner

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I think we understand your idea. There are just two comments to make (in the context of the UK).
1. You need a refrigeration unit to produce your cold water (unless you live next to a mountain stream). So it costs you.
2. Your radiators will be dripping water all over the floor and may not cool the room very effectively, in any case (they would need to be near the ceiling).

Why do you think it is not done already if it such a good idea?
 

sooyeah

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I think we understand your idea. There are just two comments to make (in the context of the UK).
1. You need a refrigeration unit to produce your cold water (unless you live next to a mountain stream). So it costs you.
2. Your radiators will be dripping water all over the floor and may not cool the room very effectively, in any case (they would need to be near the ceiling).

Why do you think it is not done already if it such a good idea?

Teathing problems 
 

Offline rosalind dna

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Why not open the windows instead of using the air-freshenrs, easier and it is free too.

That's what I do every summer, as I get a nice draft through my home.
 

lyner

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I tend to agree; air con is pretty essential in some countries if you can't build houses in the traditional way but, in the UK, wear shorts and T shirt and ignore the sweat.
As for "teething troubles" has it even been tried?
 

sooyeah

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I tend to agree; air con is pretty essential in some countries if you can't build houses in the traditional way but, in the UK, wear shorts and T shirt and ignore the sweat.
As for "teething troubles" has it even been tried?

Well exactly.
 
My idea was that cheaply, every home in Britain could have a few modifications done to the central heating system; and hey-presto, a cool home in the summer. Therefore the central heating system is set, it's all add ons.

You could however design a totally new system. But I don't think either idea, has actually been experimented with.
 

lyner

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Have you ever done any plumbing?
You would have to provide drainage from every radiator in the house; gravity operated would be unlikely to work. How would you arrange for that? And what about the poor efficiency of the system. And have you considered the capital cost plus the running cost, bearing in mind that it would be very inefficient?
The heat circulation system is the least of the problems associated with air con.
 

Offline tanveer10

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Hi

I am interested in this topic.

Sooyeah - have you had a chance to experiment some of the suggestions? What was the outcome of the same?

Thanks
 

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