From memory mine is rated at 300w max ( ie boost ) and as low as 75w depending on what i’ve set it at. So possibly your actual consumption is considerably less.

I have my MVHR plugged in to an energy monitoring remote control plug (a Kasa KP115)
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.

Grab the power display of your smart meter, look at the reading, turn the MHRV off, look at the reading, turn the MHRV back on, look at the reading.

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).

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.

I have a Vent Axia Sentinel Kinetic PlusB with a dedicated power monitor attached. Its fan speeds are 25% in the day and 15% at night, night is defined as 0000 to 0700. I'd have to go hunting for a period of boost (50%); it is seldom used, but it does run up some between 0700 and 0800 as humidity rises in the bathroom

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

Sorry, what's a duty cycle in this context?

Well surely if the summer bypass stops hot air during the day entering the house ,and so warming it , the unit is helping to prevent internal temperature increase, likewise as you say allowing cooler nightime air through the unit will possibly reduce internal temps a bit overnight. Again a totally unscientific personal view is that a combination of insulation, humidity control and ventilation all contribute to making the interior less unpleasant on a very hot day in comparison to a home that doesn’t have these. Whereas someone used to living in a fully airconditioned home would find mine uncomfortably warm.
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.

So, at last, managed (I think) to get live data off my smart ihd unit.

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.

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.

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' 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.

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...