MVHR Unit Suggestions

[Tumble]

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. 

[Savage87]

I was considering the Domus unit to begin with and in the end I found a good deal for a Nuaire MRXBOXAB-ECO2 with a display added later on. This unit is more or less the same as the Domus one.

 

I have gove through the same journey that you are about to go on back in 2019.

 

If you haven't already seen it, have a look at this:

Good luck, feel free to ask any questions.

 

[IGP]

I installed a Vent Axia Sentinel FH in my 1930’s semi in a cold loft and it’s performing quite well. I just wrapped everything in insulation (photo without everything fully insulated). 

[Ajn]

I designd ours around the smaller version of the Domus HRX. The spec said it would do 150sqm. Always found this a strange number as it should be about volume.

That said it works well as our L shape annex is 98sqm. The unit is in the utility area as we don't have a loft. Main pipe work is 125mm dia galve spiral steel for  the main runs and 100mm onto the room inlet/extract. All the extract pipe has rubber sealed joints. All joints both inlet and extract are also sealed with rubber tape then ducked tape.

Main lounge/kitchen has two ins and outs. two bedrooms and long hall have one in and out. All these provid flow across the room. The on-suite and toilet off the hall only have extract terminals with a 10mm gap under the doors.

The unit runs at 75% for boost, about 30% for CO2 purge and about 15% for normal operation. I set the flows from the terminals to give the building regulation requirements. this was at 30%. There is a C02 monitor in the system so I rfuced the fan to 15% and with 2 or even four people the CO2 is stable around 400. I think the purge comes in around 600 which has not happened yet. 

The kitchen, toilet (shower) and on-suite (shower) each have a umidity and temp sensor. Rh seems to be maintained around 45%. Towels in the bathroom dry quite nicely without any heat.

 

Efficiencies vary from about 93 to 98% dependent on outside temps. 8 and above outside it is around 95-98%. Below 3 outside it drops off quite a lot as would be expected.

 

Now the downside:

I can only descibe the so call "Bluebrain" controller as shite.  The clock is not maintained after a power cut of any sort. If you miss a short one in the night it can be days before you spot it. Next is the filter timer, that is it, it is just a timer nothing more, no cheking of reduction in air flow. The filters do need to be cleaned every couple of months. A simple task if you can get to the unit.

The 100% bypass stated is not in reality in terms of temperature 100% bypass.  While thay may say the heat exchanger is 100% pypassed but the unit as a whove it is not. Air still goes in and out of the unit and as for the most it consits of a big block of polystyrine. So on bypass the incomming air always gains a few degrees. Less is gained on boost.

 

Getting around the "bluebrain" problem:

Using my own sensors (based on D1 mini micro controller and ESPEasy) sending data to a Raspberry pi with MQTT and node-red I have added a D1 mini in the Domus controller as it fortunately has a number of inputs and outputs that can be switched/monitored. This added D1 also has a temperature sensor in each of the four pipes going to the Domus as well as the CO2 module.  The bypass proccess takes much more account of the outside temp and time of year giving  nice cooler night time flow unless the underfoor heating comes on and bypass is stopped.

So while the original controller is still 100% in the backgroud to meet the "what if anything happens to me" requirement. My controller overlay allows much more control.... and a clock that is always correct.

 

Finally you do need the set the terminals correctly after working out the flows for each room, the standard building regs can be used to do the calcs. Just work out what each room needs, (allowing flow under doors if needed) add them up and set the unit to provide that flow. Then a cheap airflow meter and some cardboard works fine.  Once you have the terminals in the ballpark you may need to adjust the overall air flow and go around the terminals a couple of times. Then set to boost and see if your bathroom/tichen extracts are above the minimum. We have eleven terminals  and it only took a couple of hours. Remember to record your data ech time so you know how it is looking and a final set with calculations that looks posh with a dated and scribbled signature that the building inspection can look at and put a tick in his box.

 

Just my view...

[JohnMo]

9 hours ago, Ajn said:

Getting around the "bluebrain" problem:

Using my own sensors (based on D1 mini micro controller and ESPEasy) sending data to a Raspberry pi with MQTT and node-red I have added a D1 mini in the Domus controller as it fortunately has a number of inputs and outputs that can be switched/monitored. This added D1 also has a temperature sensor in each of the four pipes going to the Domus as well as the CO2 module.  The bypass proccess takes much more account of the outside temp and time of year giving  nice cooler night time flow unless the underfoor heating comes on and bypass is stopped.

So long as the fans run as required, at a constant rate (we exchange air at a rate of 0.3ACH) and you have a manual boost button, nothing more is really required. Auto boost, time clocks, not needed. In winter the humidity is likely to be too low rather than too high. For example today outside is 2 Deg and 99% percent humidity, inside 20.5 and 39.5% humidity. Last time I used boost was because we had 10 people in the lounge.

 

Check/clean with hoover the filters every 6 months, replace with new every 12 months. Forget it's there the rest of the time.

[Tumble]

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 

[Eric]

I installed a Vent Axia, very pleased with it. The humidity sensor worked well.

Personally I don’t know why you need an app, it just runs 24/7 & you have humidity sensor & boost switch/controller.

[Savage87]

my unit Nuaire unit has a humidity sensor on it, but it's basic. I have another humidity sensor is the bathroom which is connected to an ESP controller and it boost that way.

 

You are overthinking it, the boost switch can be done via so many wireless options you just need to decide what would work best for you. I also boost via another ESP controller via wifi.

 

@Ajn could you please let me know what model sensors are you using for temp, humidity and CO2? I'm currently using some DHT22's, BME280, BME680 and Xiomi BLEs

[IGP]

The WiFi bit isn’t needed, save your money. Once it’s setup it’s basically leave the unit to it. I’ve clicked the boost button once on Christmas Day with family over.

I just leave the integral humidity sensor in the unit increase and decrease the fan speed in proportion to the humidity increase from showers etc. 

 

[Mike]

Ideally stick to one of the models independently tested for the Passivhaus Institute: https://database.passivehouse.com/en/components/list/ventilation_small. The 'efficiency ratio' is the overall measure, taking into account heat recovery + electricity consumption.

 

Passivhaus certified units come with a more realistic measure of their performance compared to non-certified units (Paul have a short explanation).

 

 

 

Edited January 13 by Mike

[Ajn]

On 11/01/2024 at 22:39, Eric said:

Personally I don’t know why you need an app,

You don't ... or my wife doesn't. But I do, it is fun to play, learn new stuff. Need something to do when the football results or strickly come ice skating is on.

[Ajn]

On 11/01/2024 at 22:57, Savage87 said:

ould you please let me know what model sensors are you using for temp, humidity and CO2?

MH-z19 for co2 and BMx280

[MikeSharp01]

On 11/01/2024 at 21:41, Tumble said:

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 

Think it does support all the connectivity you need on the ECO B models - best to call their technical help line - great advice and the unit is made in the UK I think.