I bought a plug in energy meter, what I wanted was a meter which included time, well I suppose really the reverse one which did not include time, a watt is a joule per second, what I wanted was to measure joules rather than watts, although since we tend to use a weird unit called a kWh that was good enough for me. 360 seconds in an hour so 360 joules = 1 kWh this is a metric system?
Anyway whole idea is to see over a set time how much is used. It is near impossible to work out how much is costs to wash cloths, as the power used goes up and down during the wash, with the plug in meter I could find out the cost of doing a wash, and any other item which switches on and off. So when brewing beer I could work out on a very cold day I needed 5 watt average to maintain the fridge temperature to 20°C so I then knew I could use an 8 watt bulb to maintain the temperature, I did not need a 20 watt heater, by reducing the size of heater I also reduced the hysteresis so there was a valid point in measuring.
Be if a faulty freezer, or working out size of heater the energy meter has a use. However to have the energy meter connected to whole house is rather pointless, yes you have used 5 kWh in 24 hours, but you really have no idea what used those 5 kWh, you can read the power something uses from the label, what you can't read is how long it uses that power for.
Since all gas is used by central heating then with gas it is different. But with electric too many items are on the same meter for it to do any good.
Even central heating, it would be nice to know how much can be saved by better controlling the temperature of each room. However my attempts at controlling individual rooms temperatures showed it's not that easy, with a fan heater you can quickly heat and allow rooms to cool, but fact you are moving the air around means you could be losing more energy, with radiators without a fan, switch it off and it can take hours to cool down, and hours to heat back up again, we see efficiency ratings of electric heating based on this idea, so 100% efficient is a radiant heater aimed at people in the room only on when room occupied, however there is a control problem. So if a room is used for 4 hours, and it takes an hour to warm up, then 4/5 = 80% efficient. Use the room for longer and efficiency goes up.
So take a room not used after 8 am until 10 pm i.e. bedroom and if you can turn off the heating for part of that time then you save money, but it also gets heat from rest of house and takes time to heat and cool, so if set to 18°C and it cools to 16°C then take a centre point so work on what is saved by cooling room for 1°C for 14 hours, it is actually very little saving, but the point is a meter working out what all rooms use, is going to tell you nothing, what you want is a meter recording room by room to be able to use the information to do any good, if you can work out it will save £20 per year to allow room to cool and re-heat it, and the device required to do that will cost £40 then you know you will get your money back in 2 years. But cost of heating whole house is useless, it does not give you anything which can be used.
Well, if there weren't progress, we'd still be putting shillings in the meter.
