ASHP - Investigations and calculations

[Andy]

The Epc estimated energy usage isn’t a very accurate figure at all. My house is about 130 square meters of living space with a lot of exterior wall as it is a converted smiddy. Plasterboard with glass wool insulation sagging all over the place. I calculated my heat use in two ways

I used an iPhone in my boiler and recorded the audio wave form so I could see the time on/off. It is very easy in any audio software to measure time on/off. This only works with an on/off boiler. Ones that modulate the flame up/down wouldn't work for this process. Before hand I set the flow rate as low as it would go which also gave me an idea of which rooms needed radiator improvements. I also left the boiler on continuously for a day to simulate a heat pump. Then I could compare the outside temperature and wind against oil usage. Knowing the nozzle size I could use the manufacturer spec to calculate the oil and therefore energy usage. It was pretty accurate. The main thing I have found is that on the very cold days is generally quite calm and so in an older property you will find the heat pump comfortably heats at much lower outside temperature then the mcs design spec. For example I was aiming for -6 degrees but when we hit-15 a few years ago it was working flat out but keeping up. The thing you need to do then it’s take quick showers to avoid heating water.

I also used the mcs spread sheet to calculate the energy usage s has been mentioned. Before I find the sheet I had also worked it all out from first principles as I am a geek . All the figures came to ball park the same as the boiler tests.

I am using a 12kW Nibe gshp which maxes out at about 16 amps. Note that often the hot water heating cycle doesn’t use the rates output. For example mine only gets about 6kw average throughout a hot water cycle.

I’d recommend trying out the oil boiler thing as the weather gets colder. It’ll give you a good idea of your pipe work will be able to transfer the heat.

With regards to wbs. We use ours a lot less than we used to. The point of the heat pump is to leave it on all the time. If you the light a stove it gets very unpleasant very quickly in one room. The central thermostat detects the extra heat and the heat pump throttle back. Then a lot of rooms are cold and the one with fire is hot. Take care in placing the thermostat so it isn’t too close to the stove.

[Andy]

For those wanting a feel for how the cycles work in an inverter based GSHP heat pump here are some screen shots of the graphs for earlier in the year. You can see the COP as well which you can compare against a heat pump. I have radiators in my property. It may give something to compare against. We had bore holes put in so it didnt' need as much ground being dug up. I have colour coded blue blocks which are when the hot water is getting satisfied.





This is the last two days.The brine in the last 2 days is running about 6 degrees steady state. About 8 degrees oat is about the temperature the heat pump starts cycling as it won't throttle back any further.





There is a set back temperature during the night and I also charge the hot water as much as possible in the afternoon cheap rate. The afternoon hot water charge stops the heating until the tank is up to temperature.

[Andy]

It also works out the annual kWh use of ~30,000kWh heating & hot water, but this is based on 'degree days' which seems to be a slightly old fashioned concept, with no reference to actual room temperatures, only days on which you are likely to need heating (if it is <15.5 degrees outside).

The heat loss is proportional to the temperature difference. So for every degree for example my house loses about 400-500watts. So if you know the degree days for your area then you can multiply 24*degree days*temp per degree to get the energy required in the year. This isn't the energy required to run the heat pump as its COP varies with temperature. Try and get the manufacturer specs to see the COP at colder temperatures and make sure the device will output the heat at that temperature without immersion addition if possible.

[AGT]

Nice work, love hearing about different solutions, like the iPhone trick!

[richbee]

Rich,
Do Octopus run a vac test on your house or would you benefit from paying to have that done? I see the idea of low&slow working well on the HP but I think I'd also want to improve where I could after a leak test. Just a thought but maybe not practical?

We noticed huge differences across the home when actively hunting down leaks. There were SO many it would be embarrassing to list (maybe 60 to 80 leaks addressed).

The whole heat up/ cool down timings radically shifted in our favour. I didn't have a leak test performed but did multiple runs through the house clipboard in hand and over time addressed all that I could. Didn't cost much other than time but the returns were (are) insane. 1982 barrett bungalow extended 3 times.

I don't know, but I guess not - the quote just says "Our Surveyor will perform a detailed assessment of your home that allows us to prepare your final system design"
It is a good idea - we've done some work on leaks, especially in the 80's lounge with suspended floor, an open fireplace & non-insulated cavities

[Joeboy]

Rich,
Do Octopus run a vac test on your house or would you benefit from paying to have that done? I see the idea of low&slow working well on the HP but I think I'd also want to improve where I could after a leak test. Just a thought but maybe not practical?

We noticed huge differences across the home when actively hunting down leaks. There were SO many it would be embarrassing to list (maybe 60 to 80 leaks addressed).

The whole heat up/ cool down timings radically shifted in our favour. I didn't have a leak test performed but did multiple runs through the house clipboard in hand and over time addressed all that I could. Didn't cost much other than time but the returns were (are) insane. 1982 barrett bungalow extended 3 times.

I don't know, but I guess not - the quote just says "Our Surveyor will perform a detailed assessment of your home that allows us to prepare your final system design"
It is a good idea - we've done some work on leaks, especially in the 80's lounge with suspended floor, an open fireplace & non-insulated cavities

I wouldn't think they would, more likely a tickbox scenario. I find the idea of the HP fascinating. I might have a crack at working out my own place in Scotland for kW req's. Is there a generic calculator to use?

I also bought another 3 rolls of the 1.5mm insulation strip we used at daughterlys in Edinburgh. The leak sealing makes such a difference as its 24/7 switch off. I'll be going back round our place next week.

Are you booked for a surveyor?

[richbee]

The Epc estimated energy usage isn’t a very accurate figure at all. My house is about 130 square meters of living space with a lot of exterior wall as it is a converted smiddy. Plasterboard with glass wool insulation sagging all over the place. I calculated my heat use in two ways

I used an iPhone in my boiler and recorded the audio wave form so I could see the time on/off. It is very easy in any audio software to measure time on/off. This only works with an on/off boiler. Ones that modulate the flame up/down wouldn't work for this process. Before hand I set the flow rate as low as it would go which also gave me an idea of which rooms needed radiator improvements. I also left the boiler on continuously for a day to simulate a heat pump. Then I could compare the outside temperature and wind against oil usage. Knowing the nozzle size I could use the manufacturer spec to calculate the oil and therefore energy usage. It was pretty accurate. The main thing I have found is that on the very cold days is generally quite calm and so in an older property you will find the heat pump comfortably heats at much lower outside temperature then the mcs design spec. For example I was aiming for -6 degrees but when we hit-15 a few years ago it was working flat out but keeping up. The thing you need to do then it’s take quick showers to avoid heating water.

I also used the mcs spread sheet to calculate the energy usage s has been mentioned. Before I find the sheet I had also worked it all out from first principles as I am a geek . All the figures came to ball park the same as the boiler tests.

I am using a 12kW Nibe gshp which maxes out at about 16 amps. Note that often the hot water heating cycle doesn’t use the rates output. For example mine only gets about 6kw average throughout a hot water cycle.

I’d recommend trying out the oil boiler thing as the weather gets colder. It’ll give you a good idea of your pipe work will be able to transfer the heat.

With regards to wbs. We use ours a lot less than we used to. The point of the heat pump is to leave it on all the time. If you the light a stove it gets very unpleasant very quickly in one room. The central thermostat detects the extra heat and the heat pump throttle back. Then a lot of rooms are cold and the one with fire is hot. Take care in placing the thermostat so it isn’t too close to the stove.

Thanks for those ideas, Andy - good to know that yours can manage at -15 from a design goal of -6. Not sure about this idea of using the WBS less though - where's the fun in winter if you can't light a nice fire!

Thinking about how to measure the oil usage, I have Tado radiator valves, which give you an monthly usage estimate for M3 of (assumed) gas and cost for heating. I guess the gas quantity could be transferred into kWh pretty easily, maybe needs a slightly different % efficiency assumption. It also records a graph of individual room temperatures and when the boiler is on for each room - but not sure how I could output that data from the app. A quick web search suggests that there is an API which can be interrogated using a Github script.... but that's slightly past my knowledge level

[richbee]

Rich,
Do Octopus run a vac test on your house or would you benefit from paying to have that done? I see the idea of low&slow working well on the HP but I think I'd also want to improve where I could after a leak test. Just a thought but maybe not practical?

We noticed huge differences across the home when actively hunting down leaks. There were SO many it would be embarrassing to list (maybe 60 to 80 leaks addressed).

The whole heat up/ cool down timings radically shifted in our favour. I didn't have a leak test performed but did multiple runs through the house clipboard in hand and over time addressed all that I could. Didn't cost much other than time but the returns were (are) insane. 1982 barrett bungalow extended 3 times.

I don't know, but I guess not - the quote just says "Our Surveyor will perform a detailed assessment of your home that allows us to prepare your final system design"
It is a good idea - we've done some work on leaks, especially in the 80's lounge with suspended floor, an open fireplace & non-insulated cavities

I wouldn't think they would, more likely a tickbox scenario. I find the idea of the HP fascinating. I might have a crack at working out my own place in Scotland for kW req's. Is there a generic calculator to use?

I also bought another 3 rolls of the 1.5mm insulation strip we used at daughterlys in Edinburgh. The leak sealing makes such a difference as its 24/7 switch off. I'll be going back round our place next week.

Are you booked for a surveyor?

Not booked yet - I'm hoping to get someone round next week to look at cavity insulating the 80s part of the house before the survey - I think it would be better to have the insulation in place, rather than size the HP based on no insulation and then alter the way everything is calculated to work - maybe....

In terms of the calculation, I was given the MCS excel sheet from 2015 by my neighbour. You are very welcome to a copy of it if you like. It's not the most intuitive sheet in the world, but sure you could work it out

[MrPablo]

This is a useful resource I've been using to guage the impact of various insulation jobs.
It's allowed for a quick room by room approach throughout the house.

https://openenergymonitor.org/heatlossjs/

[Fintray]

I wouldn't think they would, more likely a tickbox scenario. I find the idea of the HP fascinating. I might have a crack at working out my own place in Scotland for kW req's. Is there a generic calculator to use?

You can get a one-off survey access to Heat Engineer software for £12, I think it was worth the cost as it gives you loads of options and ends with a comprehensive report. The parameters can be altered many times so it's not like once you have completed your survey that is it, I altered the maximum flow temperature a few times to see how the existing radiators would perform.