Yes good point @djh, Glyn’s peak heat demand over 24h this winter coincided with a return from being away and outside conditions being around 0. E.g the big spike in consumption Jan 15th onwards here: Emoncms - app view dashboard
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Can’t disagree with most of that.
The 9Xth percentile heat demand is what we’re after.
It’s driven by a combination of air temperature and windspeed.
Custom and practice is (I think) designing to air temperatures alone; whilst using typical air change rates.
Using limit condition air temperatures AND limit condition windspeeds over eggs things if these are independent events.
This problem largely goes away if you accept a little supplemental heating at design condition.
From a system perspective (investment in peak grid capacity) you may well be better wasting energy during mild weather when solar is coming out of your ears in order to ensure that you never need direct electric heating at design condition that will stress the grid.
Better still use wood burners or mini split air conditioners not oil filled radiators for that peaking.
That’s also better from a general purpose everyday resilience perspective. (can still heat with that AC and an immersion if the monobloc goes pop whilst it’s snowing out and the spares are sunk by the Houthis etc)
Reheat from frost setback is maybe an issue. Mitigations include materially higher output from the heat pump at lower flow temperatures and higher output from emitters at lower room temperatures. And you probably don’t come home during a design condition event and probably do have the option to set the heating the day before remotely.
At some point hot water heating must limit?
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Really great to see this integrated, I’ll start piping my CO2 sensors into emoncms!
I have a 30 year old prefab house with a moisture barrier, so my ACH when keeping windows closed is around 0.1 or less (CO2 half life in my living room is 8 hours). I’m using CO2 sensors + notifications from Home Assistant to open the windows when air quality gets bad. This way I’m also not blowing too much heat out the window. It will be interesting looking at wind speed and correlating it.
For the heat loss surveys in Germany they (have to) assume 0.5 ACH if no measurements are available. That’s also the value they have to target for designing ventilation systems for new houses. I already found 0.5 quite high since in the survey that accounts for around 30% of my heat loss. Seeing rates of 2 or higher seems crazy and it’s no wonder that this might lead to oversized heat pumps.
Especially heat pumps should in my opinion be sized according to their modulation range to best cover the histogram of expected heat loss at the installation site within that range. Allow around 5% of the lowest expected temperatures to fall outside of the max power and then cover those with a backup heater if it’s needed at all. The next step down from my 10 kW unit would have been 3k€ cheaper. At current electricity rates that would be 10000 kWh. I very much doubt the backup heater would use that over the lifetime to cover the few extreme cold snaps. Take increased wear&tear due to cycling and economically it makes no sense whatsoever. My heat pump had to be sized for -12°C! All that power sits there unused for 99.9% of the time. I’ve had one day this year with a -10°C average and that was a rare event.
Both the regulatory & installer side need to completely rethink their approach. With gas heaters being able to modulate to 5% of their peak power oversizing isn’t too bad, but with a mere minimum modulation of maybe 30% coupled with the fact that they output more heat when it’s warm, heat pumps need to be treated differently.
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Thanks both, appreciate the perspectives on this!
That’s really interesting! is a blower door test the recommended measurement over there? How common is it to measure vs assume?
Lots of good points there @Andre_K, optimising for the histogram, great! I’ve heard a lot of stories of badly configured booster/backup heaters coming on far to early but that’s more of a commissioning/manufacturer control issue, agreed if very carefully controlled especially if it’s windy with lots of wind power available then that could make a lot of sense.
Would be great to see how well the app works for you! and anything you can share on integrating CO2 data from the sensors you are using would be welcome!
Nice work @TrystanLea et al.
As you now from a little while ago, I changed to using “effective temp” to compensate for the windy weather.
Even though my house is over 200 years old, it’s not very leaky (we had the blower test) but still it’s noticeable because the wind blows straight into the walls of the house.
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Yes good point @MyForest how much wind related compensation do you need to add? and what was your blower door test result?
That algorithm is literally all I do. It is then used to drive the weather compensation as you all do every day already.
Unfortunately our blower test person never sent the report so we had to go from what we remembered him saying which was that we had leaks equivalent to 1m x 10cm across an external area of about 200 metres squared (or was it 1m x 30cm…hmmm). His summary was that it was surprisingly not-leaky. That’s because we filled lots of gaps to stop the mice getting in, like this:
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You never measure with an old/existing house and they just assume the default value of 0.5 stated in some DIN norm (might be different for different house age, unsure about that). When you’re building a new house you’ll have to get a blower door test and pass it if you want to be eligible for the myriad of subsidies towards energy efficient houses. But those houses will have some form of controlled ventilation with heat recovery.
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What would be the best way to get my legacy CO2 data in there? I can get it out of Influxdb in any shape I need but am just wondering how to best get around 2 years of data in there.
Weather comp needs a smoothing setting IMO 
E.g adjust based on average outside temp over 12, 24, 36, 48 hours perhaps?
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Can you get that data in CSV form? If you can arrange in timestamp, value csv format e.g you could use the import tool on the feeds page:
Otherwise it’s more of a scripting task to fetch data from your current database and forward to the api…
I sure can get it in csv format but in the past I’ve had some trouble with feeding in larger amounts of data like that (with a certain number of data points it just locked up). But I’ll try again.
Definitely needed. It makes no sense to adjust flow temperature for the 2 hour super cold portion of the night, especially with heat still stored in the walls. The time constant for smoothing should be related to the intrinsic heat loss rate of the building. I will probably implement something like that on my Vaillant unit over ebus next winter since I have all the basics of the heat pump covered now. New project needed…
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Yea it is crazy that it’s not standard to do this… I drop my flow temp overnight but see lots of systems increasing flow temps on weather comp…
Daikin has averaging option for the external thermostat, but 0, 12, 24, 48, 72 hours… 6 Hours seems like a more reasonable period but its not an option.
My old school ground source unit has the thermistor in a sealed box not exposed to air. (mechanical damping)
Fridges used to do the same (sensor with a similar temperature response to a vegetable)
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Sun and cloud? Or boost events on mvhr?
Typical Scotland - every type of weather on one day. Ventilation rates don’t change that figure much and it was constant anyway.