Electricity Saving with ASHP

My Air-Source Heat Pump (ASHP) is either on or off, being controlled, in the final instance, by a switch in what I call my engine room (contains all the gubbins for the solar PV, solar thermal, ASHP, the underfloor heating manifold and the 500 litre water tank). 

The underfloor heating has been off this winter in order to save on electricity, as I have written before. However, the ASHP was still running 7 x 24 in order to keep the domestic hot water system providing hot water. 

Now, running the ASHP 7 x 24, just for domestic hot water, costs quite a bit of money - it uses upward of 2-3kW when kicking in. It struck me that I'd be better running it during the day (when I'm more likely to need hot water) and when I'm at least making free electricity through the solar PV system and the temperature is warmer than at night. Better still, I really need to run it only on sunny days and during the hours I'm generating maximum solar power, being an hour and a half either side of midday, so as to minimise cost. Added to that, sunny days kick the solar thermal array into action, taking the strain from the electricity. Ideally I need the solar thermal to kick in for an hour or so to raise the water temperature (which can be 40 degrees, even in winter) and only then start using the ASHP to take it to 50 or 55 degrees.

I did this manually, switching the system on and setting the hot water temperature to 50 degrees (far hotter than I normally run it for the underfloor heating, which is about 40 or 45 when really cold). On really sunny days, like we've had recently, it can raise the water to the required temperature within an hour and the heat captured easily lasts till the next morning, sufficient for a couple of showers. The cost is nothing, as the electricity generated from the solar PV system is free, as is the heat from the solar thermal.

As an aside, I can use whatever electricity I generate with no penalty on the feed-in tariff - I could use 100% of what I generate and yet still get its value from the feed-in tariff..

Doing the switching manually is a pain, as I have to be home to switch the ASHP on and off, so I thought it would be ideal if I could automate the process. To do it properly, switching the ASHP on when sufficient electricity is being generated to run it, would require some fancy monitoring electronics that are beyond me, but I could get a fair simulation of this with a programmable Smart Switch.

I first decided to do an experiment with a Smart Device I already have -  a Smart infrared panel which I bought for the new workshop. I moved the IR panel to the AirBnB room and connected it to the house 2.4GHz network - these Smart devices all run on 2.4GHz only and not 5GHz, which is a bit of a pain, but 2.4GHz has greater penetration of walls than 5GHz, so it makes sense.

Using the Tuya Android App I created a programme to turn the heater panel on between 10:30 and 13:30, only if it's sunny and the temperature in the AirBnB is below 19 degrees. The Tuya App monitors the local weather where it's sited through the Interweb and the IR panel monitors the room temperature itself automatically, which provides a feed to the App. Given it can be sunny at 10:30 but cloudy by 11.30, I made 3 separate programmes, each for an hour long, so the weather is checked 3 times over 3 hours. Just to be safe, I created an extra programme to ensure the panel is switched off at 13:33.

It worked - I used only self-generated electricity. On the basis of this I rigged up a Wi-Fi extender to get 2.4GHz Wi-Fi to my engine room and purchased a Smart Switch from Amazon for £20.90 (I got a 2 gang switch to allow room for expansion into other automated switching applications within the engine room, such as the Gold Pump, which pumps the domestic hot water around the house). 

I didn't think the switch handled the full load of the ASHP, being merely a relay to the control box with a 3 amp fuse in it, so replacing this with a Smart Switch suitable for lighting purposes was assumed to be completely safe (it wasn't).

These Smart Switches have huge protuberances on the back, but the switch backing that was already in situ could easily accommodate the extra depth and fitted the front plate perfectly.

Installation wasn't a doddle, as the existing switch, when I opened it to look at the wiring, is a double pole, for which the received single pole switch wasn't suitable. A double pole switch doesn't work just on one wire, but both, being in-line with two triple cables (L, N and E) and suited to high power applications, such as cookers and water heaters (the latter being the application).

The single pole switch could work, theoretically, by connecting the live wires and inserting the single pole switch into the neutral circuit, but it's not recommended, added to which the single pole switch had no earth connections.

So, I returned the Smart Switch to Amazon and sent off for a double pole Smart Switch (cost £19.99 plus £6 delivery), which took a couple of weeks to arrive.

Two lives, two neutrals, but no earth, not that it needs an earth. The two earth wires just need connecting with a block to maintain the earth circuit. Here it is in position.

And here's the automation profile in the Tuya App.

A scene to switch on between 11am, but only if it's sunny, and a scene to switch off at 1pm, regardless. And it works.

I also ordered a couple of Tuya compatible Smart Plugs, with which to programme the living room lights to go on 5 minutes before sunset and go off again at 9pm, when we go to bed. A bit geeky, I know, not to mention high in capital cost, but I love to try out tech. Sadly, they were a bit shit and one packed up within a couple of days. It's worth getting reliable brands.

The thrust of this post is that ASHPs are fine, if you're using them to heat the house in winter, but inefficient if leaving them on 7 x 24 solely for domestic hot water.

As an aside, given the double pole nature of the switch I used on the ASHP, it strikes me that I can also use one to automate our cooker, which is one of those huge Redfyre jobs, which doesn't have time controls. A Smart Switch fitted instead of the existing one would allow me to set the cooking temperature manually before leaving the house, with a programmable Smart Switch turning it on and off at the required times, or remotely at a time of my choosing.

Naturally, the weakness of all this Smart technology is that it's hackable, so don't go switching on my ASHP just for the hell of it.