With all the advice floating around about ways to cope with extreme heat, I was idly wondering if freezing water in an external freezer (not internal because that just heats up the room) would serve as a cooling mechanism when brought indoors.
So what is the (rough) amount of ice required to cool a smallish room (say
3m * 3m * 3m for ease of calculation) down from 30C to 22C?
I assume that the ice starts at -18C, and that there is an extra effect when the ice turns into water (latent heat of thingie?) but I have brain fade at the moment.
I've checked for room coolers with ice packs but they seem to be a humidifier (not good long term) with an additional ice pack.
I am also assuming that this is not a long term plan (unless you buy in your ice) because the average freezer could take up to 24 hours to get a large volume of water down to -18C and putting too much in could just thaw your frozen goods.
Having said that, there is potential to amalgamate the contents of two chest freezers and use one purely for ice making.
All in all, it looks as though lashing out around £450 for a portable aircon might be a more practical way to go if there are likely to be yet more heatwaves this year (and beyond).
Latent heat of fusion, which is 70 calories/gm for water. That is the major point at which energy is required. To get ice at -18C to +22C requires 18 calorie/gm up to zero, 70 to melt it, and another 22 to get it to +22C.
Your question's a bit vague. Just cooling the air, or the walls too? How much wall thickness to cool and what's it made of?
It is a bit of a nebulous question. To answer you would first need to know the rate of energy gain for the room from its surroundings.
Counter intuitively this means doing a set of heat loss calcs for the room. i.e. working out how quickly heat leaks through it, and how many air changes there are in it per hour.
Once you know that, you know the rate of energy removal from the room to maintain an equilibrium temperature. The greater the difference you want to maintain between the room and its surroundings, the higher that rate will be.
See:
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for how to calculate.
Note also that it is a deeper question that just temperature, since relative humidity will have a large effect on the perceived comfort in the room, not just temperature. So efforts that lower temperature and raise RH in the room, may not achieve any perceived benefit.
Now when you know all that, it still does not translate into an amount of ice as such, but you could work out how long a given amount of ice would "last" at the rate of energy input. Even that is not a simple sum since the maximum rate of energy transfer into the ice will be continuously falling as a result of the reducing temperature differential between the room and the ice.
Yup ice has a specific heat capacity of around 2100 J/kg.c, water 4200. The latent heat of fusion is about 334 kJ/kg
The question would come down to what the maximum cooling power of the freezer is. If it is less than the rate of gain of the space you are trying to cool, then it will not be possible to cool the space continuously without reducing the rate of heat flow into the room.
A proper air to air split system might be a better bet. Then it can be a top up heating solution for winter as well. Also much quieter and they work much better than the monoblock units since they don't have the same design limitations.
I thought they used BTU/hr, but turns out you're right they used to use tons of ice:
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1 ton of ice (907kg) is defined as 12000 BTU/hr. A typical portable air conditioner is 9000 BTU/hr, so 605 kg of ice melting over 24h, or 25kg ice per hour.
I suspect that would be rather a lot to make in a domestic freezer. (whose output might only 200W or so)
The best way and one the BBC are at last advising, is one of using the mass of the house to keep you cool. You have a means of measuring the temperature outside plus inside, then when the outside is lower than the inside you take advantage of it by ventilating the house.
I have been doing that for years and it mostly works. Generally that will involve opening windows on an evening, then closing them next morning. During the night the good cool airflow, will cool the fabric of the house down, then during the day the cool fabric will keep the interior cool.
I also have the side door of the house open during the day, to permit some fresh air in, but have a fly screen there. Flies don't tend to come in through open windows in the dark and I only open the first floor windows. Opening ground floor windows would be a security risk.
The above works perfectly for most weather in the UK, but in this exceptional heat, then I use a second method...
A large fan, with several wet clothes hung up in front of it, can pull the room temperature down by several degrees due to evaporation, but you need to be sure of good ventilation to avoid the humidity increasing. That method is much more effective than ice blocks, because there is more area for the fan the evaporate.
Last night I had two front bedroom windows opened wide and one at the rear. At 16:20 my indoor temperature is a comfortable 22.3C, so no need for a fan - outdoors I am measuring 27.2C.
Well one ton of ice ovr 24 hours is apparenlt equivalent 3.5kw of cooling, which is oddly the rating of my air con unit.
So I would say you need more ice than a domestic freezer can produce. This makes sense when you compare the power requirements of my air con and a standard freezer....
My split load is also 3.5kW cooling capacity, and I'm interested to know how it's going to cope in a room 6m x 3m x 2.4m (which includes ~250W of computer kit).
It's reached 38.8C outside so far today and is still maintaining the 22C set temperature inside. I did just pop outside and the outside unit wasn't running, so it's not at full duty cycle yet.
I have kept the curtains closed which will be reducing the normal heat gain into the room (solar gain from sun through the windows is often the largest part of the calculation of heat to be removed by aircon).
So far, it's used 3.01kWH today, costing 95p. At this rate, today will be the most expensive so far this year by the end of the day.
This is just a back of the envelope capacity analysis, to give some idea what "class" devices fit into. The electric power they use, is a measure of capability. Your mileage may vary, of course (not all devices have the same SEER). I'm not trying to be an HVAC engineer here, just give some idea what is "reasonable".
ton = 12000 BTU
chest freezer 500W
10000 BTU portable AC 1000W 6000, 8000, 10000 BTU units
2 ton house (central air) AC 2000W 1.5, 2.0, 2.5, 3.0 ton 1.5 ton equals 2200 sq ft, very approximately A "sealed" non-drafty insulated house needs less
When the central air fails (no refrigerant inside), the 10000 BTU can "hold the temps down" in one floor of a house, but it just runs flat out. You can put the portable AC in the kitchen, open the kitchen door, run two box fans in hallway, to mix kitchen air with other rooms. Maybe temp is 75F-78F or so. It's not cold, but on the other hand, you're not dying. Part of your "comfort" comes from dehumidification, part of the comfort from temperature reduction. When the far end of the house receives solar gain, the box fans cannot transmit enough cool air to that end of the house, for the scheme to work. But at night, the temps will equalize a bit. The purpose of the box fans, is so participants in the house think you are "sharing your good fortune".
If the 10000 BTU is isolated to a single room, it might be "too cold" in the room, and then it will cycle thermostatically. The reason there are 6000, 8000, 10000 BTU units, is for "right-sizing" the units and getting decent dehumidification. But you can also adjust the number of rooms the unit services, to adjust the "capacity equation".
If each bedroom has a window AC for example, a small bedroom may receive decent dehumidification with a 6000 BTU unit. If you use a 10000 BTU, it drops the temperature so fast, there is no time to dehumidify the air. The air is then "clammy" and uncomfortable. You want a 3-5 hour run on the window AC, to dry out the room air (preferably 5 hours). So right-sizing is important for permanent installs, where the bedroom door will be closed. Usually the text on the box, indicates approximate room size.
The reservoir must be emptied on the portable AC, once or twice a day. Part of the comfort comes from reducing air humidity by condensing out the water. The water flows to the reservoir tank. With window AC units, the condensate water just drips outside somewhere.
My central air, has a drain line running from the A-coil and the circulation fan box, to the sump pit. And the sump pump, pumps the condensate water to street level. During an AC run, the sump pump, pumps at least twice from the condensate collected.
You cannot leave a portable AC running for long periods, without fitting a drain line to a floor drain somewhere. Use larger-than-needed drain line, to avoid the drain line plugging and flooding at the source end. What you want, is drain lines with rise-over-run, so the drain line does not develop mold inside (from standing water and room dust) and plug with mold.
If you are present in the room when the portable AC runs, you can drain it when the overflow shuts the unit off. I recommend draining the tank before it is completely full, so you won't spill it :-) Can you tell I have experience ?
You always figure out where the drain water is going, when making a sub-ambient cooling solution.
And no, the typical home dehumidifier box, is *not* for hot weather. Dehumidifiers are a "loser" in this sort of weather, and are not to be used. All a dehumidifier box does, is make "hot stinky air". You'll be sorry :-)
For best performance, refrigeration devices should be dumping their heat outside. On portable AC units, there are "one hose" and "two hose" units. The "two hose" unit makes sense from a science perspective. Think carefully about how a one hose unit works, before buying one. It pumps the now-cool house air... outdoors. Some one hose units may have the hose split into two air paths, but that is somewhat unlikely. But it is very hard to find two-hose units. They are not as common.
The general topic of AC can involve theft and building security issues, which you have to think about. Window AC boxes sometimes get stolen by pranksters. Sometimes they just want to climb in, through your window and do a break and enter. Make sure any installs of that type, "look robust" to scare off the druggies. If it looks like the unit will just "fall out", that's not as good.
Even fitting a two-hose portable, to a "window gap", invites break and enter. A window which cannot be physically opened all the way, is an asset. Some theft rings use a "small kid" to fit through gaps in your house armor. Fools have even tried to enter through chimneys... and got stuck.
When using a portable, you have to "put away your toys" before heading out in the car. Secure the house before you leave and so on. It takes good solid well-thought-out installations, to make an installation permanent (or seasonal). Maybe you want to unbolt your window AC when winter comes, so the window can be insulated for lower winter heat loss.
Or don't have any toys to start with, for the handful of *really* hot days we get, just go out for a long drive in the car with your shorts on and aircon set to "LO"
Hmmm. I was pondering how long the aircon on my car would run before the battery went flat (not wishing to disturb people with a running engine). It would make a nifty emergency work-from-home office.
It can be belt drive. It can have a clutch, so it can be disengaged for thermostatic control purposes. That's on an ICE vehicle. The belt continues to turn, but the compressor does nothing if the clutch for it is disengaged. The pulley and belt design, suggest it draws two to three times as much mechanical effort from the car, as a 1kW alternator.
On a BEV, it can be an electrically powered unit. Not all BEVs have a heat pump though. They put a heat pump in a BEV to control battery temperature, and cabin aircon is a side effect of having that subsystem. (They can cool the battery, or they can cool you.) When shopping for a BEV, you need to ask questions about this. To avoid surprises.
Which made me think, how do they work in electric cars? They're quite power hungry (I'd guess a kW compressor - I can just about feel it cutting in and out as it slightly impacts engine power output).
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