Heating cost

[Andrew Gabriel]

Been thinking for a while how to get heating costs logged in home automation data. Toying with how to read gas meter automatically. Then it dawned on me that, in one case, there's a non-modulating Potterton Profile boiler, so the energy rate is going to be pretty constant when the gas valve is open. Indeed, it's 18.1kW after checking a timed run against the gas meter. So, I added a relay across the gas valve coil, and started recording the burner on time.

Only going for a nearly week so far, but this is what I have:

Date burner on Energy Cost (HH:MM:SS) (kWh) (£.p)

10 Dec 1:03:41 19.21 0.67 11 Dec 0:00:00 0.00 0.00 12 Dec 3:59:06 72.12 2.53 13 Dec 5:13:14 94.48 3.31 14 Dec 2:02:02 36.81 1.29 15 Dec 5:05:19 92.09 3.23 16 Dec 1:27:22 26.35 0.92

10th only records a partial day from when I had the relay connected. There was no one in on 11th, so no heating came on.

I'm going to graph this more accurately with house temp, outside temp, heating on, and call for heat signals, all of which I already log, but I thought figures above were interesting even by themselves, even though you can't tell how long the heating was on from them.

[Dave Liquorice]

Presumably your HA system had a spare input that just need a config change to monitor/log? I'd sort of like to see when and for how long the boiler fires here but the logging machine would be a PC, located

20m or so away from the boiler so not that easy to interface to. Maybe this is the project to hang getting an Arduino off. B-)

[Andrew Gabriel]

Yes - I have 48 inputs, 40 of them currently in use. I can expand this system up to 64 inputs by buying more modules (newer systems can go significantly higher).

10 years ago when replacing all the floor coverings, I flood wired the place with alarm/HA cabling (and Cat5e), and there are still a number of unused cable runs. One ran past the boiler and isn't ever going to be used for what it was originally intended for, so I repurposed it.

This was earlier this evening. While I was out (and the heating was off), the loft dropped to almost freezing, which causes the HA to switch on the central heating to prevent pipework in the loft freezing.

Dec 17 19:12:13 Temperature - Loft 1.0 Dec 17 19:12:14 Input Loft Temperature LOW Dec 17 19:12:14 Output Heating ON Dec 17 19:12:14 Send Output Heating Demand ON Dec 17 19:12:15 Output Heating Demand ON Dec 17 19:12:33 Input Boiler Burner ON Dec 17 19:25:22 Input Boiler Burner OFF Dec 17 19:27:33 Input Boiler Burner ON Dec 17 19:29:19 Input Boiler Burner OFF Dec 17 19:32:01 Input Boiler Burner ON Dec 17 19:33:40 Input Boiler Burner OFF Dec 17 19:36:25 Input Boiler Burner ON Dec 17 19:38:07 Input Boiler Burner OFF Dec 17 19:40:58 Input Boiler Burner ON Dec 17 19:42:42 Input Boiler Burner OFF Dec 17 19:44:01 Temperature - Outdoors -4.0 Dec 17 19:45:41 Input Boiler Burner ON Dec 17 19:47:20 Input Boiler Burner OFF

I've looked at those once or twice, but never played with one. I did buy one of the NETIOM modules from CPC when they were on special offer. It's a while ago now, but there was something about it which was not ideal - IIRC you can't make it send a message when it gets an input/interrupt, so you have to poll it from the host, severely limiting the resolution achievable. It would be fine to generate lots of outputs, but I have loads of spare outputs in the existing system.

[dennis]

Is the pipe work actually in the loft space or just above the ceiling? If its just above the ceiling you can remove the insulation below the pipes and insulate over the pipe work moving it into the warm zone and making it unnecessary to put the heating on so early. Obviously you have to do the same to the tanks if they are there.

[Andrew Gabriel]

Well above the ceiling. There's no insulation under the tanks, but the pipes extend beyond this area. They are insulated, but that doesn't prevent freezing long-term.

I actually find the idea of heating the house just to protect the loft very stupid. I have thought of putting a heating circuit in the loft as a zone of its own with a set point of 1C. It would probably just consist of a long pipe snaked around at the floor level. However, if something goes wrong, it would be the first thing to freeze, and I don't want that to do any damage, or prevent the rest of the heating system working. One thought is a separate pump and isolated circuit, which drains back into a tank just below the ceiling (top of airing cupboard) when not running. Then I step back and think heating tape would be simpler.

[dennis]

If you only need to keep it above zero it makes sense. There are usually other things in the house that you want to keep warm, plants, pipes, pets, etc.

A loop of plastic pipe would do the job and it doesn't burst when frozen or at least that's the claim. Maybe you could run it around the other pipes like trace wire?