air conditioning - How much BTU? After several years of living in Italy i am now wanting to install air con in certain rooms of my home. Trying to look into how powerful system i need. I have found these calculations that you should consider. You need to know The floor area of the room The size and position of windows, and whether they have blinds or shades The number of room occupants (if any) The heat generated by equipment The heat generated by lighting Floor Area of Room The amount of cooling required depends on the area of the room. To calculate the area in square metres: Room Area BTU = Length (m) x Width (m) x 337 Window Size and Position If, your room has no windows, you can ignore this part of the calculation. If, however there are windows you need to take the size and orientation into account. South Window BTU = South Facing window Length (m) x Width (m) x 870 North Window BTU = North Facing windows Length (m) x Width (m) x 165 If there are no blinds on the windows multiply the result(s) by 1.5. Add together all the BTUs for the windows. Windows BTU = South Window(s) BTU + North Window(s) BTU Occupants You will have to take that into account people who normally working in the space. The heat output is around 400 BTU per person. Total Occupant BTU = Number of occupants x 400 Equipment Clearly most heat in a room is generated by the equipment. This is trickier to calculate that you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is probably safer to overestimate the wattage than underestimate it. Equipment BTU = Total wattage for all equipment x 3.5 Lighting Take the total wattage of the lighting and multiply by 4.25. Lighting BTU = Total wattage for all lighting x 4.25 Total Cooling Required Add all the BTUs together. Total Heat Load = Room Area BTU + Windows BTU + Total Occupant BTU + Equipment BTU + Lighting BTU This is the amount of cooling required so you need one or more air conditioning units to handle that amount of heat. Can anyway else think of other things you need to take into consideration?
"Can anyway else think of other things you need to take into consideration?" Errr, yes, well, quite a few. Like the 'U values', and orientation, of walls and roof (or ceiling) and the volume of the room, and the ventilation rate (if you don't have any control over this). And perhaps it would be easier to work with KW rather than BTU.... Tell you what Chill - I bet andy can sort this in a jiffy: call in your debts! You sort his website, he sorts your a/c calculations. Alternatively, approach from the other direction: how much are you prepared to pay in running costs? Get something with a rating which you can afford to run.
Andy help with this one. Too many things to calculate its confusing! Yes, your right i intend to buy class A energy rating equipment.. I have read somewhere (cant remember now) that if you have a too powerful system then the dehumidification process does not work very well and it can shorten the life of the compressor. How true this is i do not know but i'll wait and see what Andy has to say. Ive seen in the shops: 7000 BTU 9000 BTU 12000 BTU 18000 BTU I think i just need one 7000 BTU Upstairs and one 12000 Downstairs. I'd rather have the 2 seperate systems as one is for downstairs and one upstairs. ( day / night.)
This might be useful/up to date or not. Anyway, several years ago I decided to put air-conditioning in a) the main bedroom, and b) the sitting room. The cheaper option was to put one powerful "engine" outside with two "blowers" inside (with one in either room), but instead of that, on the advice of the bloke who installed it, I opted for the slightly more expensive option of having two separate engines outside, a bigger one for the sitting room (12,000 whatever they ares, I think, for about 10x6x3 cubic metres), and a smaller one for the bedroom (9,000 things, I think, for about 5x5x3 cubic metres.) It was (only very slightly) more expensive, but that arrangement had three big advantages: 1. If one "engine" or "blower" or remote control broke down or the batteries were flat or whatever, I'd always have the other; 2. The engines could be attached to the wall very close to the blowers, so that the tube between each engine and its corresponding blower could be as short as possible. I was told that this makes the things work more efficiently; 3. I saved on electricity. With my original plan, the powerful engine would have been working whenever either room had to be air-conditioned. As it is, during the siesta (the most important time, I think), only the smaller one is busy. This also meant less wear on the engines, of course. The only advice I'd add is a) to get a personal recommendation for the people who're going to do it - i.e. find somebody who's got a system that they're pleased with, ask who did it, how long it took to actually install (about eight hours for me, I think), how good the service was if needed, etc, b) to do it now (i.e. well before the summer, when they'll be busy), and c) to take the advice of the bloke who knows. He'll come round for a preliminary look and discuss it and say what he thinks. S
I'm fascinated by this BTU rating thing. I was not aware (though it looks likely) that the US also use BTU (since domestic a/c is a bit of a US thing) and maybe Japan also use this measurement of power. Tomorrow I will look up a BTU - KW conversion in 'a book' (which I know I have downstairs): though andy has posted a site where you can convert it. I am very old, but I never had to encounter BTU even as a schoolchild! I met Horsepower (and I know one of these is 746W, which seems to be a pretty weedy horse to me) - but BTU seems to me to be a sort of consumerist thing designed to confuse the masses....wots wrong wiv watts?
Its all kind of confusing init BTU? However, The amount of power consumed is measured in KW/H I belive the BTU is the term for the amount of heat the air con can extract. For example lets take 2 aircon units both 12000 BTU One consumes 3.1 KW/H Class A The other 3.3 KW/H Class B I know that the energy class is the amount of power consumed to do the job (cool up to 12000 of BTU) Andy, Can you explain anything on this?
BTU's and all that!! BTU is the British Thermal Unit. It was very common pre 1973 and also is still relatiely common for rating boilers etc. Although since the UK adopted the SI system of notation, has not been taught widely. As with most imperial measurements, the BTU is a bit difficult to work with. Firstly, it is an instantaneous measurement. Meaning that a direct conversion into watts (joules/second) is not possible. The conversion factor from BTU to joules is 1059.67 The conversion factor from BTU/hr to watts is 0.293 It actually makes sense that the measurements you have been given are not in fact rated in BTU's, but BTU's per hour. Meaning that the ratings are as follows: 7000 BTU = 2051 Watts 9000 BTU = 2637 Watts 12000 BTU = 3516 Watts 18000 BTU = 5274 Watts Anyway, to calculate the size of unit you would need, you could calculate the following: 1) The fabric heat gains through roof and walls 2) The solar heat gains through glazing 3) The heat gains due to the rate of air change and infiltration of external air 4) The heat gains due to equipment (PC's, TV's etc) 5) The heat gains due to occupation (About 100watts per person) Then once you have done this, you simply add them all up and your unit is sized. Regards Andy PS: Alternatively, you could take 100-150Watts/m2 and that should be OK.
C'mon twanks - talk dimensionally: is BTU equiv to KWh or to Kw? From what chill has posted he thinks it's KWh...he could be right. I'm feeling horrendously ignorant because I can't approach BTU empirically.
Lax, I have typed this slowly to help you understand!!! OK. short sentences required I see!! BTU cannot be converted to Watts, kW, kWh or any other time related unit. The BTU it would appear is an instantaneous value of energy. It can therefore be converted to the joule. If you then take the BTU operation over a period of time (BTU/hour) as in the example above. This means you can convert to the Watt which is in fact measured in joules per second. If you then run that Watt for an hour, you get the energy consumption in Wh kWh. If it was the case that the units given were in kWh, then it would be the most useless piece of information to put on the side. Also, my experience with boiler ratings in BTU's, which is limited, it aint in kWh. It's a bit like trying to say if i have five apples and take two away, how many oranges have i got left. Unless the units have the same basis, they cannot convert. Andy
Hi all, Thanks for replying all, I bought a 9000 btu class A machine over the weekend for the bedroom. Things have already started to heat up here in the north of Italy hitting 26'c today. I've got a guy to install it which will hopefully happen next week all being ok. I calculated the room size and most of the factors above and a 7000 btu was my option (bedroom). I could not find a class A 7000 btu machine in offer so i opted for the 9000 btu instead.
Hello Sanch, Yes all was installed fine and works a treat! Only use it in the night as the humidity gets very high here but it certainly makes a difference to sleep well in the hot summer months!
Bringing up an old thread i know but..... I moved house at the end of last year and i'm wanting to install my old 9000 btu machine in my living room which is 5 * 4 metres. It's not massive i know, but it does me just fine. So is a 9000 btu machine good enough to cool this size room or should i upgrade to a slightly bigger 12000 machine? I already have a portable 12000 machine which i plan to use when things get really hot ( and it does in July) for the rest of my apartment but my main concern here is the living room. Anyone have a similar size room and what setup do you use? :idea:
Re: air conditioning - How much BTU? I have a 12000 set up in my soggiorno and it works just fine. If the sun shines most of the day then 9000 may not be enough.
Re: air conditioning - How much BTU? I'm impressed you even found this old thread. I have to say, though, that it made for interesting reading. Knowing those BTUs is definitely important before you buy and install.
I would go with 7000 BTU or less, but I'm not very fond of air conditioning, I like natural air better, that's why I always looks for places that have at least 2 windows LOL
Windows make very little difference in the summer months when its 30'c outside in the night. I like natural air too but the only option to sleep well is air conditioning. When the sun shines from the morning until late evening the bricks are very warm. The house is like an oven at night and even with the windows open it does nothing (no wind) BTW, i ended up with a 12,000 btu machine for my living room as it gets very hot in that part of the house during the summer months.
