Tumble

These heat exchangers aren’t working on the bulk energy of the air, but rather the local energy at each point in the exchanger. As these are contra-flow exchangers the hot extract air entering is exchanging heat with the supply air right as it exits. As the extract air progresses through the exchanger its temperature will drop as the energy is extracted until it’s basically at the external air temperature. Does that help? I’ve also found this diagram, which shows the difference between a parallel-flow and contra-flow exchanger:

Did fully insulating fix your issue?

I live in a trickle-vent house, built before airtight regulations came in, but don’t feel we get sufficient ventilation. I’ve got a CO2 monitor and it regularly goes over 1000 in our lounge and requires significant window opening to reduce. We also get a lot of condensation on windows, bathrooms, etc. So while we aren’t airtight I’m installing a MVHR to hopefully improve the air quality (and then where opportunities come up I will improve airtightness). I plan to set the background ventilation rate to be sufficient to keep CO2 in check, and then boost to the regs requirements. In summary, I hope to find the MVHR system very useful even in a non-airtight house (as is supported by other posts on this forum). Keeping the flows balanced makes sense to me in terms of reducing drawing in of external-temperature air. If it extracted more than it supplied then cold outdoor air would have to make up the difference. Keeping it balanced means the only outdoor air which will want to come in will be wind driven.

Thank you all for your input. I’m pleased to hear of positive reviews of Domus, Nauire, and Vent-Axia units. Perhaps I’m overthinking this, but it seems to me that the unit selection will be a significant factor in the system’s performance. Or is it more the case that so long as the unit has enough capacity, any will do the job fine? All I really need is a reliable quiet unit with humidity-triggered boost (to save cabling and using boost switches). I’ve trawled through data sheets and based on my original spec, this is my comparison of a number of units: Vent Axia Advance S 34 dB running @ 60%. 26 dB @ 40% Integrated humidity sensor Integrated controller which can be repositioned Integrated controller wifi (2023+ model) Frost protection 93% efficient Vent Axia FH 28 dB running @ 60% (22 dB on setback) Integrated humidity sensor No Wi-Fi Frost protection 90% efficient Nuaire MRXBOXAB-ECO2 34 dB @ 75% (24 dB on setback) Integrated humidity sensor MRXBOX-VSC controller No Wi-Fi Frost protection 90% efficient Domus HRX2D 21dB running @ 50%. Integrated humidity sensor “Smart” remote controller No Wi-Fi Frost protection 94% efficient Mitsubishi Lossnay VL-250 27 dB (~20 dB on setback) No humidity sensor Controller is extra Extra option for Wi-Fi No frost mode description 90% efficient Titon HRV 1.6 Q 27 dB running @ 65% (15 dB on setback) Not sure about humidity sensing Additional aura-t controller Don’t think supports Wi-Fi Frost mode 89% efficient I’m still leaning towards the Domus HRX2D, but the Vent-Axia Advance S provides me with the app-control I would like, but at a cost of additional noise. I’m not sure it’s worthwhile. Are there other units that I should consider? Thank you

Hello, I’m retrofitting a MVHR system into my late-90s house to improve indoor air quality and hopefully reduce window/bathroom condensation issues. I’ve selected MVHR over other ventilation options as I like the continuous operation, level of adjustability, and potential to save energy rather than increase it - and I’m up for the DIY install challenge! I’ve been reading a lot on this forum and am comfortable with my basic plan, but would appreciate some thoughts on the unit I have selected - as I haven’t read many topics weighing up pros and cons of different choices. I will be placing the unit in a cold loft, but will build a PIR box as required. I’m keen the unit is as quiet as possible and have included attenuators in the ducting design. I’m designing for about 50l/s at 100pa, would like inbuilt humidity boosting, automatic frost protection, small enough to fit through a 52cm x 68cm loft hatch, and ideally some ‘smart’ or app connectivity (but can live without). I believe the Domus HRX2D unit would meet my need - wouldn’t be running much above 50% at my estimated duct pressures and at that has a rated SPL of only 21 dB. It also includes a humidity sensor which I’m hoping will reduce my need for manual boost switches. My concern is a lack of marketing on the Domus website (that I can find) - is this still a current unit? It also doesn’t have smart connectivity, but I can compromise to its remote display. If anyone has a Domus unit I would appreciate a review, and I’d also love to hear of any highly rated alternative units.