Last couple of summers we've had extended periods where my flat can reach a pretty uncomfortable temperature to work in. I do not want to install AC and have so far managed to counteract it by making sure my windows are open overnight to circulate cool air and by closing different curtains + blinds through the day (one half of my flat gets morning sun, the other half evening sun). This keeps the air in the flat comfortably below the outside temperature, but if I forget to do either of these steps the temperature can creep up a bit and it's not possible to cool it down until evening (and if it's super humid and hot it might not cool that much).
I'm wondering if there's any low-energy or green solutions to this. I suspect I'm asking for something impossible or that the only way to improve this is to automate the blind opening/closing :-/
If you live in a cold climate, buy a mini-split (a type of AC that also works in reverse).
ACs are very efficient (more than 100%!). By using an AC to heat (a Delta(T) in my city of at least 30C) your home in the winter you more than offset the carbon to cool and dehumidify it a mere 5-10C (again, in my case).
Heating a home in cold climates are far worse than cooling, but there's a puritan rejection of AC:.
- The Delta(T) is larger to heat a home than to cool it. Delta(T) sets the heat loss through your walls.
- There is an attitude that cooling is hedonistic, while heating is a necessity, but it's thermodynamically and metabolically far easier to heat than to cool.
- Most heating is done with fossil fuel furnaces which are at best 90-95% efficient. A heat pump can be over 300% efficient [1] (i.e. it moves 3J of heat from the cold side to the hot side using only 1J). This is much better improvement in performance than an electrical car.
Get an AC that can work in reverse, and if you want don't use it in the summer.
EDIT (added following):
[1] The metric here is coefficient of performance, COP = Thigh / (Thigh - Tlow). For 30C to 20C the theoretical maximum is 3 000%, or 30x
Wow ok by an interesting coincidence I’m actually needing to upgrade my heating too (everyone moved off the building’s shared boiler, then voted to get rid of it at the one meeting I missed - hats off to them). Installing a new gas boiler and fitting it to the existing system means ripping up some of my (beautiful old and recently refurbished parquet) flooring so if this gives me a way to avoid that AND maybe cool the air relatively efficiently during the worst summer days I’ll definitely need to look into it!
Study it a bit while it's still warm and look up your local weather. [1]
The COP gets worse as Delta(T) increases and heat pumps are nowhere near the theoretical best, so at a certain point it's better to use gas. But that's typically below 0F (-10C).
I put in a four way Mitsubishi (2x as expensive but super silent) in my old home. Relatively happy with it, except I don't think the installers put enough coolant in it (it's best to instal a heat pump on a cool day). The air does gets a bit dry, so consider getting a heating humidifier for the night.
Finally, if you can afford it and if you can install it, a heat-pump with buried coolant lines really multiplies the efficiency (since the ground is above freezing and acts as a heat store through the seasons)
EDIT:
[1] If you live near a large body of water, especially if it's salty, it's very unlikely your cold days are cold enough to be a problem for the AC. Unless you live in Thunder Bay.
[2] AC is not a huge climate problem. Heating, cars, global supply chains, agriculture are bigger problems. AC just gets the attention because it's considered frivolous. A bigger problem is that modern homes are built with no consideration for cooling. My old house was 100 years old and naturally kept cool. My new house has at least 7 seven!!! skylights. It's impossible to cool. At least 5 of them face north :S
Yeah i'm in central europe which is somewhat approaching continental climate - so bitter winters and toasty summers (not quite as bad as some parts of Ukraine and Russia ofc). But I'll def read into it, I'm glad I at least have another option even if it might not work out. Thanks!
In Massachusetts, homes with mini splits always have another heat source for when it gets cold enough that the efficiency drops. It’s more like 20F even though technically the devices can work down to 0F. If you want to go green you can try electric baseboards and just hope you rarely use them.
No need to apologize, precision is important. Perhaps my point blurred two different things.
Point number 1 (directly referencing your question):
No, I did mean it's easier to heat than to cool. Basically every mechanism release heat, including heat pumps. Ultimately, to get a person to a comfortable temperature, all that is needed is to wrap them up in insulation until their body heat matches the heat loss for the required Delta(T).
Cooling is another thing altogether. There is no cooling mechanism, all we can do is:
Your body can do 1. but only if the humidity is low enough, but it can't do 2. My conclusion here is to illustrate that your body can largely take care of itself when it comes to warming itself up, but it's (comparatively) very bad at cooling itself.
Point number 2:
While heating is very easy, it's also very energetically wasteful for two reasons:
1. The Delta(T) you have to fight against is larger, often double so the losses are larger (Delta(T) sets the heat loss of your home)
2. Most heating isn't done with heat pumps which are very efficient, whereas all cooling is pretty much only done with heat pumps [1].
3. You can use heat that the AC moved around. Today you can hook up your AC to your boiler so the heat you moved out of your home is dumped into your boiler. As long as you use enough hot water, the more you run your AC the lower your carbon emissions will be since the water boiler runs off gas (I'm not advocating for using more hot water, btw)
So, while using your AC is not good for the climate, it is not the easiest optimization to do first.
[1] Swamp coolers are weird: you live in an arid enough place that evaporating water cools you down... so you waste that precious water when you could just run an AC???
It is in fact thermodynamically and metabolically far easier to heat than to cool.
We're warm-blooded creatures, so if we want to be warmer we can just jump around, or put on insulation. To cool, we have to sweat, and if the sweat can't evaporate much because of high humidity, we have to do a lot of it.
Similarly, if we want to heat a space, we can just burn something. Cooling requires active transport, whether finessed by something like a windcatcher or attic fan, or through an air conditioner.
Heat pumps are more efficient, but more complex, than furnaces, and can be run in reverse to provide air conditioning.
People really don't appreciate how brutal humidity is on our bodies' ability to cool down.
I run my AC more to dehumidify than to cool. I hate setting my AC below 78, that's freezing, but I have to because of improperly sized AC units, poor HVAC installation, etc.
My thermostat is located in a cooler part of my house compared to my bedroom -> my thermostat has to be set to 73 to cool my bedroom to a nice T.
If my AC is very large it wont run very long between cycles. When it does it will wring every bit of moisture out of that relatively small amount of air.
If the AC were smaller, the AC would run just about all day long, more of the air would then go get its moisture removed.
In other words:
1 unit of 4C air mixed with 9 units of 30C air -> 10 units 27.4C. Assuming I've removed all the water in the one unit of 4C air the water content has only gone down 10%
5 units of 24.8 C air mixed with 5 units of 30 C air -> 10 units of 27.4C. If I can get just 50% of the air out chilled 5 units of air, I've removed 25% of the water in the air.
These numbers are just thrown at you, so take them with a BIG grain of salt. You'd have to look at the water saturation tables to really do the math.
In all the apartments I have lived (in the southern states), there was an AC that also works in reverse, it is called HVAC. However, in northern states, gas heating is cheaper than HVAC in the winter.
HVAC mean Heating Ventilation and AC (i guess). It is the name for the general problem of dealing with the environment in the house.
Second, about the Northern states.
It really depends where you are and what your AC unit is.
Some heat pumps don't have the capacity to heat a house in the North. If they're sized just right for cooling, they wont be powerful enough to heat your home [1] . As a result these units will start using resistive heating (emergency heat) which is the worst way to heat your home.
Also, there is the edge case of extremely cold cities in the Midwest (Chicago is not cold enough). These cities have some days where the T can be -20F (about -30C). Not only does the COP start to plummet, the temperatures might be outside the operating range of the coolant.
So you do have to do your homework before you install a unit.
But I live in a Northern city now, with bad lows of 0F (-13C?) and the heat pumps work just fine.
[1] In the South if you size your heat pump for cooling, you're sized ok for the heating. Even if you get a few days below freezing triggering the emergency heat, that's not a big problem.
> I'm wondering if there's any low-energy or green solutions to this.
The answer is "it depends". How your flat is designed will have an impact on what you can do. But if you are able and willing to do some house work, there is a lot you can have control over.
At the end of the day, it's all about how you can control humidity, the flow of hot and cold air and humidity. At your disposal, tools such as conductive materials, insulating materials, etc. Google "passive house" to see the concept and what these things use.
With that said. Heat pumps are incredibly efficient, and replacing your heater with a reversible air conditioner which you can then run in both summer and winter will do far more for your overall energy efficiency than anything else you can do.
Most of your energy consumption comes from winter-time heating. Start here for a good introduction to heat pumps and how they are so efficient: https://www.youtube.com/watch?v=7J52mDjZzto
Here in Norway awnings that extend automatically to shield the window from the sun are an off the shelf item, they also retract automatically if the wind gets too strong.
There was an interesting article on heat pumps in the NY Times yesterday - they are similar to AC units but far more efficient, requiring far less electricity to run. Plus they work as heaters in the winter. I use heat pumps coupled to solar panels and draw very little power from the grid, if any.
Ya, Im very confused when people talk about heat pumps as separate from ACs. My new tenant got super excited when I used the word "heat pump" to refer to my AC.
I'm wondering if there's any low-energy or green solutions to this. I suspect I'm asking for something impossible or that the only way to improve this is to automate the blind opening/closing :-/