Green Building Forum - Cost of running MHVR Tue, 19 Dec 2023 08:29:08 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302376#Comment_302376 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302376#Comment_302376 Mon, 10 Jul 2023 11:05:23 +0100 mikrt
I was comparing my electric bill with neighbours over the weekend, and mine is substantially more than theirs.

I was reminded that I have an MVHR running 24/7 along with boost periods.

The plate says it runs @ 2A.

Is my working correct please? 2A x 240V = 480W (0.48W).

0.48 x 33.37p/kWh x 24hrs x 365 = £1,403 y / £116 m, & 5% VAT too :cry:

Thanks in advance]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302377#Comment_302377 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302377#Comment_302377 Mon, 10 Jul 2023 11:42:34 +0100 Artiglio Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302378#Comment_302378 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302378#Comment_302378 Mon, 10 Jul 2023 11:54:51 +0100 Simon Still
the *fuse* might be 2A but the actual maximum power draw of the unit is only 190W. And that would be running at max power. You'd expect the fan power consumption to be fairly proportional to the % airflow setting (and the control circuitry should be fairly minimal).

Standard setting for 'normal' airflow is 30% so the default power consumption would be about 60W = 0.06kWh rather than 048

Running 24/7/365 That's 525kw/h which at current c34p per unit is £180 a year.

Theres going to be periods when it's running at a higher ventilation rate, but that should be more than offset by times it's lower (we set to reduced rate when we're out of the house)

However, the whole point is that the heat recovery bit should save you significantly more than it costs to run during the heating season, and that controlling the ventilation (rather than having a leaky house) saves you heating costs in the first place (as well as what you recover from the exact)

I'm guessing that's what the figures in another sheet are supposed to show but can't see how they've been calculated - Annual Electricity Consumption per 100m2 is 1.52 and Annual heating saved per 100m2 avergage/warm/cold 47/21/91 kWh.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302379#Comment_302379 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302379#Comment_302379 Mon, 10 Jul 2023 12:10:23 +0100 djh on position 0 (50 m³/hr) the consumption is 11 W
on position 1 (125 m³/hr) it is 41 W
on position 2 (165 m³/hr) it is 75 W

Your system may be different but I suggest that the 2A figure is a maximum and not an actual value. I suggest measuring the consumption.

Is your boost simply an increase in the flowrate or does it include some heating?

If you're concerned about your overall consumption then you need to break it down.

You can do a purely paper exercise: write a list of all the electrical devices you have, together with their power and the length of time you use them. Add them all up and see if it matches your bill. If not, think about what you've forgotten and add them in. You might also compare what you have with what your neighbour has to see if you can account for the difference in bills. Heating is usually the biggest consumer of electricity, so anything you use electrical heating for where they don't or use gas might be a clue. If they have PV when you don't that might also explain the difference, for example.

A better way is to actually measure the consumption of devices. For items that have a plug you can buy an energy monitoring smart plug like the Kasa or similar Tapo. For larger items that are wired in you can use CTs (current transformers) clipped around the wires. You can get portable meters fitted with these, or you can fit a central monitoring system such as the Open Energy Monitoring system I use. https://openenergymonitor.org/

edit: to add, as Simon says MVHR should save money overall by reducing your heating bill. So if you use gas heating you also need to compare those bills. Of course this all assumes that your houses are similar and that you keep them at similar temperatures. It's quite difficult to be exact.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302380#Comment_302380 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302380#Comment_302380 Mon, 10 Jul 2023 12:45:20 +0100 Peter_in_Hungary Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302382#Comment_302382 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302382#Comment_302382 Mon, 10 Jul 2023 14:04:20 +0100 WillInAberdeen
The step down/up in reading, is the power consumption of the fan. (Edit: can choose to see it in Watts or in £p)

If you still haven't got a smart meter, they're free and recommended for exactly this kind of thing, the early scare stories have dried up now.

Now do the same with all your other devices - router, TVs, fridge, freezer, lights, cooker etc etc and make a list of which are the heavy users so you know which ones to keep an eye on. Cooker and washing machine and towel rail in our case.

Now open some windows and turn off the MHRV, until the start of the heating season!



Simon, out of interest, the power used by the fan should be roughly proportional to the cube of the flowrate. This is because the velocity is proportional to the flowrate, the energy per litre of air is proportional to velocity², and the number of litres is proportional to flowrate.
https://en.m.wikipedia.org/wiki/Affinity_laws

Set against that, the fan may be less efficient at very low or high flowrates. So as DJH found, increasing 3x his flowrate (50->165) increased his power consumption by only 7x.

This is one reason why MHRV fans ought to be on some kind of variable speed based on humidity or CO2, and not left set on max all year (eg 0.5Ach irrespective of humidity and heating season).]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302383#Comment_302383 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302383#Comment_302383 Mon, 10 Jul 2023 14:28:29 +0100 mikrt
I've ordered a basic clamp meter to give me a better understanding of my consumption.

Will report back with findings. :bigsmile:]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302389#Comment_302389 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302389#Comment_302389 Mon, 10 Jul 2023 18:49:01 +0100 Simon Still Posted By: WillInAberdeen

Simon, out of interest, the power used by the fan should be roughly proportional to the cube of the flowrate. This is because the velocity is proportional to the flowrate, the energy per litre of air is proportional to velocity², and the number of litres is proportional to flowrate.
https://en.m.wikipedia.org/wiki/Affinity_laws" rel="nofollow" >https://en.m.wikipedia.org/wiki/Affinity_laws
.

Which means my estimate of 50% of max power being 50% of airflow is a significant overestimate - power consumption should be a lot lower than my simple estimate. I had some plug in power meters but they seem to have stopped working - might have another go at getting the display on my smart meter working.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302392#Comment_302392 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302392#Comment_302392 Mon, 10 Jul 2023 20:22:01 +0100 djh Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302394#Comment_302394 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302394#Comment_302394 Tue, 11 Jul 2023 06:29:39 +0100 cjard
In night mode, it consumes 0.0138 kWh per hour
In day mode it consumes 0.0213 kWh per hour
In an average day it consumes 0.43 kWh

Attached is an hourly dump of a couple of days in may, though there isn't much more data in there than Ive mentioned here. I never looked before, but it was interesting to note that the power factor is significantly lower at night]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302402#Comment_302402 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302402#Comment_302402 Tue, 11 Jul 2023 13:57:05 +0100 Artiglio Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302404#Comment_302404 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302404#Comment_302404 Tue, 11 Jul 2023 16:23:23 +0100 djh Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302405#Comment_302405 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302405#Comment_302405 Tue, 11 Jul 2023 17:03:51 +0100 cjard
"In no way scientific but visitors do comment on the house being cooler inside, on hot days, than they’d have expected"

Odd. I wouldn't attribute that to summer bypass per se. Perhaps you effectively cooled the house at night and your good insulation is introducing temperature increment delay. Summer bypass can't make incoming air cooler than it is when it's floating around outside the house

Summer bypass surely only helps cool a home that's warmer than the outside world. If you've done a good job of cooling the house down at night, then the heat exchanger in the MVHR will actively extract the heat from the warm supply air and transfer it into the cool exhaust air

In other word, the MHVR unit tries to preserve the state of the house relative to the world. If the house is warmer, the HX tries to keep it that way. If the house is cooler, the HX tries to keep it that way]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302409#Comment_302409 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302409#Comment_302409 Tue, 11 Jul 2023 18:46:16 +0100 Artiglio You are correct that the insulation helps prevent temperature increase , the second floor room is wholly inside the square oast roof structure, with one small south facing window, the roof is slate and on a sunny day the roof surface is too hot to hold your hand on, but you’d have no idea of this inside.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302410#Comment_302410 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302410#Comment_302410 Tue, 11 Jul 2023 20:51:38 +0100 djh Posted By: cjardOdd. I wouldn't attribute that to summer bypass per se. Perhaps you effectively cooled the house at night and your good insulation is introducing temperature increment delay. Summer bypass can't make incoming air cooler than it is when it's floating around outside the house

Summer bypass surely only helps cool a home that's warmer than the outside world. If you've done a good job of cooling the house down at night, then the heat exchanger in the MVHR will actively extract the heat from the warm supply air and transfer it into the cool exhaust air

In other word, the MHVR unit tries to preserve the state of the house relative to the world. If the house is warmer, the HX tries to keep it that way. If the house is cooler, the HX tries to keep it that wayAs Artiglio says, the MVHR does help. And it sounds like you agree with us.
During the day, when it's warmer outside than inside, the bypass is closed so as to keep out as much of the outside warmth as possible whilst providing fresh air. Most nights, when it's cooler outside than inside, the bypass opens again and actively tries to cool the house with the cooler air. As long as you haven't reduced the flowrate too much with a CO2 or humidity sensor, it has a noticeable effect and helps to control the internal temperature.
So I'm not really clear what your objection is? Nobody is claiming it does anything miraculous.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302537#Comment_302537 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302537#Comment_302537 Tue, 18 Jul 2023 17:06:05 +0100 mikrt
Nowhere near as bad as I'd feared.

With MVHR running uses 346 W, without uses 302W, So it consumes 44W/0.044kW. My average cost is 27p/kWh from next week (I'm on Octopus GO)

0.044 x £0.27 x 24 x 365/12 = £8.67/m.

Hopefully this is a much more accurate figure.

Thanks all for input.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302561#Comment_302561 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302561#Comment_302561 Fri, 21 Jul 2023 04:23:00 +0100 wookey Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302658#Comment_302658 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302658#Comment_302658 Sun, 30 Jul 2023 19:15:41 +0100 borpin Posted By: mikrtWith MVHR running uses 346 W, without uses 302W, So it consumes 44W/0.044kW. My average cost is 27p/kWh from next week (I'm on Octopus GO) What you are failing to take into account, is the heat recovered (Ventilation & Heat Recovery).

Today my Komfovent unit consumed 0.88kWh but recovered 7.93 kWh. Money well spent!

Until later this afternoon, outside temperature was 14°C. On days like this I tend to maintain as much heat inside as possible, so it is hotter than minimum. This then means the temperature overnight doesn't drop too far.

The other thing to consider, is "How much better is your inside air quality". It is not all about cost.

Higher consumption could be an old fridge, tumble dryer or dishwasher.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302659#Comment_302659 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302659#Comment_302659 Sun, 30 Jul 2023 19:27:06 +0100 borpin Posted By: wookeyOurs uses 13W on normal speed and we typically run it 10 hours/day (8am to 6pm) in winter. We turn it off for 6 months in the summer and use windows instead.As a matter of interest, do you measure CO2 levels? When I started doing so I was rather shocked how high they were, so upped the ventilation rate.

I run mine all year as it recovers so much energy and is is rare that the incoming air is hotter than inside/extract. TBH, the bypass system seems to to work too well, so when it is very hot outside, I do tend to turn it off then (open windows overnight/morning until outside is hotter than inside and then close them to keep the cool air in)!]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302661#Comment_302661 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302661#Comment_302661 Sun, 30 Jul 2023 20:13:04 +0100 djh Posted By: borpinToday my Komfovent unit consumed 0.88kWh but recovered 7.93 kWh. Money well spent!That's probably true, but only if I interpret 'day' as meaning 'time since midnight until now' :bigsmile: i.e. 51 x 24 /1000 = 1.224 not 0.88

Until later this afternoon, outside temperature was 14°C. On days like this I tend to maintain as much heat inside as possible, so it is hotter than minimum.
It's amazing how differently different houses in different places perform. Our bypass opened on 10 June and hasn't closed yet - I don't expect it to for another month or two - apart from when it's hotter outside when it switches the heat exchanger back in circuit. It's 25°C inside, which my wife noticed was identical to the temperature last year when the weather was so different. We've got some windows open today as well.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302664#Comment_302664 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302664#Comment_302664 Mon, 31 Jul 2023 08:20:26 +0100 borpin Posted By: djhThat's probably true, but only if I interpret 'day' as meaning 'time since midnight until now' i.e. 51 x 24 /1000 = 1.224 not 0.88If you do that, you need to do a similar figure for the heat recovered!

Posted By: djhIt's amazing how differently different houses in different places perform. Our bypass opened on 10 June and hasn't closed yet
I also think it is the different units and different technologies.

At 14°C outside I really would not want the bypass open! I want it recovering energy and maintaining the internal temperature.]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302728#Comment_302728 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302728#Comment_302728 Fri, 04 Aug 2023 02:13:32 +0100 wookey As a matter of interest, do you measure CO2 levels?

No. I did buy a gadget, but then changed the router it had been paired with before installing an MQTT receiver, and never got round to working out how to re-pair. And now I don;t know where I've stashed the gadget (I have too much crap lying around).

So yes it would be good, and I will one day, but monitoring has always been a long way down the priority list. My last house server died, so until that's fixed there is nothing to log to...]]> Cost of running MHVR http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302732#Comment_302732 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17894&Focus=302732#Comment_302732 Fri, 04 Aug 2023 12:30:12 +0100 RobL
https://www.digikey.co.uk/en/products/detail/amphenol-advanced-sensors/T8031/5774483

Don’t monitor it tho, except to check vaguely working as expected (blow near sensor, mvhr speeds up)]]>