Green Building Forum - Which £1k Maximum MHRV/HRV for a 80m2 Flat? Tue, 19 Dec 2023 08:41:05 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299238#Comment_299238 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299238#Comment_299238 Wed, 14 Dec 2022 15:34:41 +0000 Chendy
Any recommendations on which brands/models to look at or avoid?
Naturally, I want all the good stuff, like high ACTUAL efficiency, low cost etc.
Recondemations along this line are helpful.

But, thinking people here can provide guidance to the less google-able aspects.
Like, reliability, service support, flexibility/ability to interface with third party controls etc.

Any tips appreciated!]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299240#Comment_299240 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299240#Comment_299240 Wed, 14 Dec 2022 16:18:43 +0000 tony Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299243#Comment_299243 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299243#Comment_299243 Wed, 14 Dec 2022 19:46:57 +0000 WillInAberdeen
Default would be vent axia hr100r which is very basic. £250ish


Some high end options here https://database.passivehouse.com/en/components/list/ventilation_small]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299244#Comment_299244 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299244#Comment_299244 Thu, 15 Dec 2022 00:27:50 +0000 Mike1 Posted By: WillInAberdeenSome high end options here https://database.passivehouse.com/en/components/list/ventilation_small This is where I'd go too, though it will almost certainly blow the budget. All those on the their list are independently certified under the same lab conditions, so the efficiency they give is a good guide and you can directly compare like-with-like.

More generally, don't spec it too small - get a unit with enough capacity to run on low speed during regular use, with a summer bypass to minimise overheating.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299255#Comment_299255 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299255#Comment_299255 Fri, 16 Dec 2022 08:14:20 +0000 borpin
I can connect it to my HomeAssistant (HA) locally.

I have fitted CO² monitoring to it, but manage the fan speed by HA rather than feeding the value into it. I'd recommend some form of CO² monitoring as it is more important in my situation than RH.

Efficiency is good if the figures reported by it are correct.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299256#Comment_299256 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299256#Comment_299256 Fri, 16 Dec 2022 12:26:55 +0000 Chendy
Great, independently verified units is exactly what I'm after.

https://database.passivehouse.com/en/components/list/ventilation_small
Is the data here from testing or from the manufacturers?


I hope somebody tests the cheaper models.
Does anybody want to create a youtube channel, where people/manufacturers send theirs in to test?! ; )

@borpin
I liked the referenced to the amazing open source HomeAssistant project. I'm a electronic engineer - I will be hopefully digging into that automation stuff in due course!]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299259#Comment_299259 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299259#Comment_299259 Fri, 16 Dec 2022 14:08:18 +0000 Mike1
Posted By: Chendyhttps://database.passivehouse.com/en/components
Is the data here from testing or from the manufacturers?

The manufacturers pay a passivhaus-accredited lab to do the assessment and the database contains the certified results from the labs.

If a manufacturer chooses not to have a unit assessed, then it won't appear.

The minimum standard for all units is that they should meet EN 308:1997.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299269#Comment_299269 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299269#Comment_299269 Sat, 17 Dec 2022 09:29:25 +0000 Chendy
I will begin google for prices.
If anybody can guide me towards the cheaper brands/models in the database, that would be helpful.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299271#Comment_299271 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299271#Comment_299271 Sat, 17 Dec 2022 12:10:49 +0000 WillInAberdeen
Don't forget to price for the ducts, manifolds, valves etc and any controllers, and the labour fitting them, it can add up to quite a lot. Once you invest on all that, the extra price of a good fan unit compared to a cheap one, might not seem so bad.

There are actually some different methods in which % heat recovery can be calculated. Some say that the SAP Q method favours the manufacturers by making the performance look better, and that the PH method is more demanding. So if you have % recovery numbers quoted from different sources they might not be directly comparable, that's an advantage of the PH database.

The elephant in the room is humidity - when you draw air through the house it gets warm (sensible heat) and it carries away humidity (latent heat). MHRV units might recover 90% of the sensible heat, and their sales people talk about that a lot, that's what the testing figures measure. They don't recover (condense) much of the latent heat at all, some recover only a little condensation and some actually recover no condensation at all. (Think of this like how a condensing boiler is more efficient, only at lower temperatures so the condensing is relatively more important for mhrv). So the difference between claimed 80% sensible heat recovery and claimed 90% sensible heat recovery is less significant than it may seem, if neither is recovering much evaporative heat.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299275#Comment_299275 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299275#Comment_299275 Sat, 17 Dec 2022 17:48:01 +0000 Chendy
What do you estimate the real-world performance of these units are in a passive home then? Factoring in latent heat and any other ignored forms of energy?

I guess I guess for proof, one can see figures for how little heating energy is required in a good PH.
But I'm now curious about these efficiency numbers]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299276#Comment_299276 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299276#Comment_299276 Sat, 17 Dec 2022 17:50:08 +0000 Chendy Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299278#Comment_299278 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299278#Comment_299278 Sat, 17 Dec 2022 20:59:52 +0000 WillInAberdeen
If 1kg of outside air at (say) 7⁰/80%RH is drawn into a house at 21⁰/60%RH, then it needs:

14kJ of sensible heat (80-90% of this is recoverable by a MHRV)

11kJ of latent heat (not much of this is recoverable by a MHRV)

Try other combinations yourself with an online psychrometric chart, if of interest? AFAIK the %heat recovery testing methods don't measure the latent heat.

Other losses come from the electricity consumption, the better units use less electricity per m³ of ventilation.


For a passivhaus (or any other high performing home) you want the thermal gains from sunshine and people, to balance the thermal losses from ventilation and through the walls etc, to within an allowed tolerance, at all times of the year. If you choose a poorer MHRV, you might need to balance it out by choosing better insulation or more solar gains, that's the fun part! If you're not dealing with such a high performance building then it's more of an economic question whether a better performing Mhrv is worth the extra £ to you, and other factors like noise, controls etc.

(Edit: not at all intended to be negative about mhrv, sorry if sounded like that!)]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299280#Comment_299280 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299280#Comment_299280 Sun, 18 Dec 2022 00:35:37 +0000 Mike1 Posted By: WillInAberdeenIt's still a niche market in the UKIt is. Here in France you can buy a selection of lower-spec units from larger DIY stores, from around €750.

Posted By: WillInAberdeen...you might be able to import something from Europe cheaper.
It is worth considering this. I may well buy a PH-assessed Zehnder unit for my current project and prices - for the same unit - range from €1,750 to €3,297, depending on the supplier and the country. You may also find that model names (and their stock codes) differ between countries, so some research may be needed to hunt down the best deal, and to make sure that the prices are for the same piece of hardware.

Posted By: WillInAberdeenfactors like noise
Particularly important for a flat, if it's going to be above your ceiling or in a cupboard, Chendy.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299282#Comment_299282 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299282#Comment_299282 Sun, 18 Dec 2022 10:42:58 +0000 Chendy
I'm also totally sold on MHRV.
Watching people heat whilst keeping windows open 'for fresh area' seems insane to me.

@WillInAberdeen
More surprises, so electrical efficiency isn't factored into the declared efficiency numbers? The efficiency of the fans is ignored?!

@Mike1
Cheers, yes will be in a cupboard. Am thinking about the physical aspects also.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299288#Comment_299288 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299288#Comment_299288 Sun, 18 Dec 2022 16:40:19 +0000 Mike1 Posted By: ChendyThe efficiency of the fans is ignored?!No, passivhaus certification requires that the total electrical power consumption of all fans, controls and any essential external systems do not exceed 0.45 W/m³/h when operating at (passivhaus's assessed) full throughput, with an external pressure of 100 Pa. The best units use less than half of that, as you can see from their database.

Posted By: Chendyelectrical efficiency isn't factored into the declared efficiency numbers?
The passivhaus 'efficiency ratio' does take into account electrical efficiency, and other factors, to show 'the amount by which the energy demand caused by ventilation can be reduced.' For full details, you can read the assessment criteria yourself: https://passivehouse.com/downloads/03_Reqs_and_testing_procedures_ventilation_en.pdf

Outside the Passivhaus scheme, getting reliable numbers for either of the above is difficult.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299433#Comment_299433 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299433#Comment_299433 Thu, 29 Dec 2022 19:14:48 +0000 jms452
https://www.efans.co.uk/products/vent-axia-sentinel-kinetic-bh-right-hand-with-humidistat-and-summer-bypass-443319

Can even buy left and right to make the ducting easier!]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299434#Comment_299434 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299434#Comment_299434 Thu, 29 Dec 2022 19:41:16 +0000 cjard Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299436#Comment_299436 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299436#Comment_299436 Thu, 29 Dec 2022 19:51:39 +0000 cjard
It's MVHR..]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299441#Comment_299441 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299441#Comment_299441 Fri, 30 Dec 2022 19:18:02 +0000 borpin Posted By: cjardps.. "MHRV; Mechanical Heat with Recovery Ventilation"?

It's MVHR..IIRC we had a long discussion about that previously...:bigsmile:]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299456#Comment_299456 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299456#Comment_299456 Sun, 01 Jan 2023 20:10:00 +0000 jms452 Posted By: cjardI bought a load of temperature sensors a few years ago so I could monitor my sentinel kinetic plus B; still haven't got around to fitting them, but I really should as I've always wondered about its efficiency

the green hexagon polymeric counterflow heat exchanger is virtually the same between lots of mvhr units - circa 90% although some datasheets claim 95%!]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299580#Comment_299580 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299580#Comment_299580 Tue, 10 Jan 2023 04:38:03 +0000 cjard Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299625#Comment_299625 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299625#Comment_299625 Sat, 14 Jan 2023 09:40:08 +0000 jms452
If so it's partly manufacturing lead but also because a counterflow heat exchanger made from a highly conductive material reduces the efficiency.

Plastic can be made very thin enabling good heat transfer through the heat exchanger wall but very low heat transfer along it.

https://swissrotors.com/blog/the-battle-of-the-counterflow-heat-exchanger-polymer-vs-aluminum/]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299640#Comment_299640 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299640#Comment_299640 Sat, 14 Jan 2023 23:12:51 +0000 djh Posted By: WillInAberdeenIf 1kg of outside air at (say) 7⁰/80%RH is drawn into a house at 21⁰/60%RH, then it needs:

14kJ of sensible heat (80-90% of this is recoverable by a MHRV)

11kJ of latent heat (not much of this is recoverable by a MHRV)I don't understand this. What is the latent heat for? Where is water being evaporated? What I would expect is that the air in the building will not be at 60% but more like 40-50% where the reduction due to fresh air is balanced by emissions from breathing, washing etc etc.]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299697#Comment_299697 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299697#Comment_299697 Tue, 17 Jan 2023 16:55:10 +0000 jms452
It's the latent heat of water vapour condensed from the outgoing air into the heat exchanger.

When it's 'very cold' outside some of this becomes available.

This leads to the intersting scenario where if it's cold outside and outgoing air is high in humidity the incoming air is heated to virtually the same temperature as the outgoing air (but this is not 100% efficiency despite some marketing I've seen).]]> Which £1k Maximum MHRV/HRV for a 80m2 Flat? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299708#Comment_299708 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17667&Focus=299708#Comment_299708 Tue, 17 Jan 2023 20:44:32 +0000 djh Posted By: jms452It's the latent heat of water vapour condensed from the outgoing air into the heat exchanger.

When it's 'very cold' outside some of this becomes available.Right, but in WiA's chosen scenario it doesn't. But it's not energy consumed anywhere or lost so I'm not sure how it fits in to an MVHR 'efficiency' calculation.]]>