air con

[andy]

my idea for an air con system. any feedback would be useful

get a freezer and put a large tank inside it. fill with water (with antifreeze, unless you have any better ideas). put this in loft (if your limited for space, like me)

get a old car radiator and a water pump. pump water from tank thru radiator and back to tank. put a fan behind radiator. and you have a workin air cooler. hopefully.

so, questions.

use water with antifreeze or something else?

for gettin pipes from freezer, whats the best way to do this? drill thru side and fill gap with expandi foam?

would it also be worth adding more insulation to the freezer?

note: i will only be using this a few hours per day, mostly when i get in from work so hopefully the water should be cold enough after bein left all night and most of the day

 

[AdamW]

Ah, you have designed a "comfort cooling" system.

They are quite common in office buildings. Chilled water is pumped around the building in heavily lagged pipes, then at each vent you have a heat-exchanger and a fan. As I see it, the benefit is that the air ducts are easier to install (no need to have them going between floors etc), and because lagging pipes is easier you lose less cooling capacity.

In my experiences of using such systems, they take the edge off the heat but on a really hot day or a humid day, it isn't quite enough. Remember that an airconditioner dehumidifies air too.

This system has the advantage that the only pipes and liquids you are dealing with are safe. No nasty CFCs.

Good points you have raised
1) car radiator: this is much better for blown-air heat exchange than anything else you can commonly buy. You will need a biiiiig one. Think V12 Jag or V8 Range Rover, when you are at the breakers!
2) antifreeze: this not only reduces the chance of water freezing in the pipes, but also improves heat exchange between pipe and coolant. It also inhibits corrosion. Make sure it is compatible with copper pipes (or use different pipes!)
3) adding insulation to the freezer: little benefit to this. You might even impede the freezer by reducing airflow around the back of it.

Suggestions:
1) consider a duct-and-fan system to draw fresh air into the loft space (perhaps through an airbrick), blow it over the freezer's hot heat exchange, and extract it (through another airbrick?)
2) you may get water condensing on the heat exchanger in the room, consider how you will collect this.
3) for a fan, consider dismantling a "pedestal" fan. These are pretty quiet for the amount of air they move.
4) Can your loft support the weight of a freezer full of water? Look at the cold water cistern, you need to build something like that to support it.
5) Can you get a freezer into your loft safely? No point in dropping it on your head!
6) the freezer will be working overtime here, trying to cool something that keeps on getting warm, whilst sitting in a really hot space. You may well lug that freezer into your loft, only to find it burns out in a week.

I would recommend against it! Sorry to be a pesimist, but I think that whilst it works in theory, it won't be reliable in use or practicable to build.

 

[andy]

i might just go get a air con. altho i wanted something small to fit in an open cupboard, altho portable 1 would have other advantages...

 

[AdamW]

Andrew, you do have 2 options where commercially available kit goes...

You have 2 types of basic air conditioner for domestic use:

1) Portable unit
2) Split unit

With the portable unit (the Dalek-shaped ones you can buy in most sheds) you hang a hose out of the window or hook it into a tumble-dryer outlet. They are cheap and easy. But, they are pretty noisy, and if you have the hose hanging out the window as most people do, very inefficient.

With a split system, you have the condensor side (the "hot" side) sitting on an outside wall, and the evaporator (the cold side) sitting indoors. The two are linked by pipes that carry the refrigerant. These are the types you see retrofitted to small offices, apartments and so forth.

Now, the latter style is more expensive, but MUCH better and far more efficient, however it is really a professional-only fitting. As you seem very keen to DIY this, and as you are training in the ways of good workmanship and so forth, you could have a go at one of these. AFAIK you don't need a licence (modern refrigerants less nasty than the old ones). So, avoid lugging that freezer into the loft and get yourself a split system!

Good luck!

 

[andy]

Andrew, you do have 2 options where commercially available kit goes...

You have 2 types of basic air conditioner for domestic use:

1) Portable unit
2) Split unit

With the portable unit (the Dalek-shaped ones you can buy in most sheds) you hang a hose out of the window or hook it into a tumble-dryer outlet. They are cheap and easy. But, they are pretty noisy, and if you have the hose hanging out the window as most people do, very inefficient.

With a split system, you have the condensor side (the "hot" side) sitting on an outside wall, and the evaporator (the cold side) sitting indoors. The two are linked by pipes that carry the refrigerant. These are the types you see retrofitted to small offices, apartments and so forth.

Now, the latter style is more expensive, but MUCH better and far more efficient, however it is really a professional-only fitting. As you seem very keen to DIY this, and as you are training in the ways of good workmanship and so forth, you could have a go at one of these. AFAIK you don't need a licence (modern refrigerants less nasty than the old ones). So, avoid lugging that freezer into the loft and get yourself a split system!

Good luck!

i dont really wanna spend too much (dont have much spare cash ATM) and i wanted something small and not outside (altho my other way was big, it was inside, and i dont think freezers will work well hanging from the outside wall...)
and maybe a stupid question, but if it cools the air inside, why does it need a hose goin out?

 

[AdamW]

Well, when you cool something by an active process such as this, you need somewhere to dump the heat. The way a portable airconditioner does it is basically thus:

The unit has a cold heat exchanger and a hot heat exchanger, linked together (think like a fridge, you have a cold side in the fridge, and warm pipes on the back of the fridge)

The airconditioner sucks in air from the room and blows it over the cold heat exchanger, out into the room. This cools the room down.

In order to keep this cold heat exchanger cold, the unit is constantly pumping heat from this exchanger over to the hot heat exchanger.

To take heat away from the hot heat exchanger, the unit blows air over the hot heat exchanger. It is THIS air that is blown out through the hose.


Now, this of course is not that efficient: you are cooling your hot exchanger with air you have already cooled. It's a vicious circle. The reason it works is because the unit is relatively efficient thermally. In order to remove 4kW of heat, you supply about 1kW of electrical power.

Now, a split unit is more efficient for 2 reasons:

1) you can have the windows closed tight, keeping the cool air in
2) the air used to cool the "hot" heat exchanger is not the air you have used energy to cool down already.

So, to summarise, when cooling something down, you need to find a way to dump the heat somewhere else. The best place to dump this heat is the air outside. Feel the back of a fridge/freezer: it will feel warm. This is heat from inside the fridge, combined with "wasted" energy from powering the compressor, the fact the insulation isn't 100% efficient and so forth.

Think of a car engine. The engine is hot. You want to keep it cooler, so you pump water through it. If you want to keep your engine block at 90 degrees, you need to pass the water through a radiator so it can lose some of its heat and be recirculated.