A recent report from the Committee on Climate Change warns that as average temperatures rise, the UK faces a new climate and many homes will need air conditioning to cope.
With a lot of older housing built for colder climates, many of our homes face extreme heat, especially with the increasing number of heat waves each year. By 2050, heat waves are expected to last longer and be hotter.
As the Committee on Climate Change pointed out, it’s not just about air conditioning; passive options, such as shading, should also be considered. Passive options are often overlooked by the mainstream press, and I think there is a general consensus that simply installing air conditioning is the best option. This is not the case. To achieve the best possible effect, a combination of tactics is necessary.
Stop the sun before it heats up your home
I have an extreme example: my garden office. My garden office faces south and its facade is entirely glazed: French doors with two side windows. They have double glazing, which helps keep the heat in in winter, but in summer, or when the sun is shining, they are a huge problem.
Infrared rays from the sun penetrate through the glass and heat the objects inside, then the air, which has nowhere to escape. On a relatively cool but sunny day, say around 16°C, it can easily be 20°C inside my office. On a very hot day, it gets incredibly hot inside: I’ve seen the temperature reach 48°C, and it can only get worse as temperatures rise.
Air conditioning seems to be the solution, but it’s not as simple as you think. I’ve tried many portable air conditioners, vented through a sealed window, and they work when the weather is mild.
As soon as temperatures rise and the sun shines directly, air conditioning can slow the rise of heat, but it cannot stop it, and it certainly does not make the environment more pleasant.
I’ve used interior blinds and even UV films on the windows, but they are largely useless: once the heat gets in, it’s trapped. The answer, I found, was to use exterior blinds. Rolling them keeps the sun out and keeps the temperature at manageable levels; if it’s hot, the air conditioning can do its job and cool the room when needed, but I often find that I don’t need it.
Similarly, in my mezzanine bedroom, the front of the house faces south, so the sun shines through the Velux and makes the room too hot. Sometimes the handles are hot. I purchased external sunshades, which fit on the outside of the Velux window and reduce heat through them.
Yes, I still need air conditioning when it’s really hot, but the blinds reduce the amount of cooling needed.
Exterior shutters, rather than blinds, can be even better, and this is what you tend to find in hot countries, along with overlapping shading. In my house they would be easy to use, as I have sash windows so nothing sticks out.
Modern casement windows are harder because they open outwards, so once open you can’t close any shutters. But there are many smart external blinds that can be controlled remotely and would work, since you can operate them with the windows closed.
Air conditioning is expensive to run
Although modern air conditioning systems use heat pumps for maximum efficiency, electricity costs make them expensive to operate. And the more heat they have to handle, the longer they have to run, which increases costs.
More AC also means more strain on the grid, and not all of that energy is clean energy, helping to produce more fossil fuels and more CO2.
There are calls from some places to combine air conditioning with solar panels, powering the units with clean, free energy, but that’s not without its problems either. As noted earlier, solar works well if you have a south-facing roof; if you’re in the shade, in an apartment, or have an east/west roof, you get little electricity, or it’s not worth having it at all.
There is also a big difference between properly installed split air conditioning units and portable units. Split units, with the condenser outside, are much more efficient than portable units, and you can run multiple vents from a single external unit.
Split air conditioning is more expensive to install and there is the problem of knowing where to place the large outdoor unit. Coming back to the problem in the UK which has a large number of older homes, especially Victorian terraces, there is very little space to install the outdoor unit.
In fact, one of my neighbors just had air conditioning installed, and the large external compressor is outside the front door, covered but still clearly visible. In my house I could not install air conditioning, because there is no room for the outdoor unit.
Then there is the question of what to do if you want to install a heat pump for your hot water. Many split air conditioners are air-to-air heat pumps, so they can cool or heat a room, but they won’t heat your radiators, underfloor heating or hot water.
It is possible to get one system that will do everything, but it is not common. So in most cases you might end up with a heat pump for hot water and a separate system for air conditioning. Where are all these units supposed to go?
Cool inside, warm outside
Air conditioning does not cool a room by blowing cold air; instead, these systems use a heat pump to move heat from one location to another. In this case, they suck heat from the inside and expel it outside, as explained in our guide on how portable air conditioners work.
This ensures that all the warm air in your home is pumped to the outside environment. According to the Royal Institute of Chartered Surveyors (RICS), in urban areas with many air conditioning units, the impact at night can be a temperature increase of 2.5°C. So as we cool our homes, we heat the outside, which means more cooling is needed, and so on.
The RICS goes on to suggest that new buildings should adopt passive techniques to avoid overheating, and that allowing plenty of space for vegetation can help: trees are a good way to cool urban spaces and create shade.
Do not aim for refrigerator-like temperatures and limit use
Once air conditioning is available, people tend to use it more. And people often want to cool rooms to very low levels, to get that freezing cold feeling. Both of these are false. Air conditioning should be used when necessary, not when it feels good, and higher target temperatures should be used.
I tend to set my portable air conditioning to 23°C when using it on the hottest nights. It’s cool enough to sleep in and reduces the amount of energy used by the AC unit.
There is no single solution
The situation is going to get hotter and hotter and air conditioning is only part of the solution, but certainly not alone. New buildings need to be designed to be thermally efficient and reduce the need for air conditioning, while older buildings need help: better insulation and shading to prevent the sun from shining through large windows (natural and artificial via blinds).
These passive techniques cannot completely prevent a home from becoming too hot, but they lower the maximum temperature reached and, therefore, the amount of air conditioning that must be used.
For more insights on this topic, visit Here.
“`
