Cool!

So, we're in for another heatwave. I'm alright (Jack) as I have my aircon unit upstairs; however, it got me thinking about a few things.

Firstly, Hay has a hideous habit of opening windows and doors in the evening, even when it's still blisteringly hot outside, and I'm constantly arguing with her about why she insists on doing this. I remind her of the 2nd Law of Thermodynamics and, as a scientist, I expect her to understand, which she steadfastly refuses to do, even when I let her try it once and we ended up sleeping in an oven upstairs. I will only open doors when the temperature of the patio outside our French doors drops to either the same as, or slightly lower than the inside temperature (I have an infrared sensor), and it works. Any air coming into the house first has to pass over the patio and, if it's warmer than inside, it will heat the house.

The major problem we have, as I've said before, is that with the vaulted ceiling upstairs, combined with black, slate roof tiles, the heat builds up, even with the layers of Celotex, with nowhere to escape because of our bad window design.

Secondly, I'm doubtful about the old wives tale of hanging up a wet towel or blanket to aid cooling. A room in a house is a closed system and the 1st Law of Thermodynamics states that, within a closed system, energy cannot be created or destroyed, except converted to another form of energy. If the evaporated air could condense and then be decanted outside the closed system, then yes, there would be a cooling effect, but not otherwise. Also, a wet towel would increase the humidity, making it uncomfortable.

Thirdly, it seems pointless to me to be running an air-source heat pump on cloudless days in summer, when the solar thermal system heats the water to scalding temperatures. Yes, it will work overnight and the dawn, but we use little hot water then and it doesn't take long for the solar thermal to kick in.

The other day I ran the aircon for most of the day, but the air-source had tripped. My electricity usage was less than a day when the air-source is running. I'm going to keep the air-source switched off while we have the heatwave, as I'll be running the aircon most of the time.

Fourthly - tinted windows on cars. While they can block light hitting the interior, they get damned hot themselves. I would hazard an educated guess that for a car with a light coloured interior, such as light grey or buff, they heat the car interior, whereas with a dark interior they would aid cooling by reducing the absorption of heat by the seats and fascia, despite their intrinsic heating.

I performed an experiment on my Ford Galaxy yesterday, which has deeply tinted windows in the back, and here are the temperature readings after leaving it in the sun (side ways onto the sun) with the windows shut:

The inside temperature on the headlining throughout the car was 46 degrees.

Front: clear glass 45, seats in sun 65, seats in shade 42

Back: tinted glass 55, seats in sun 40, seats in shade 40

It does show the tinted glass gets 10 degrees hotter than clear glass and a prima facie justification for tinted glass in a car with a black interior, although I need to find a similar car to mine with no tints to do a comparison.