Up and running

[Coanda]

Finally got the DIY MVHR running yesterday. It's just taped up to make sure everything fits.

 

Today I checked everything over and fitted thermometers.

 

Here's what it looks like after running a couple of hours.

 

[Coanda]

42 views and no comments.

[ToughButterCup]

Drop in at my place and check mine over when yer driving south on the M6 from Cairn Ryan .... Are those numbers  (or rather the differences between them) what you'd expect?

[JohnMo]

So is this MVHR unit you made yourself?

 

What are the temperature sensors you used?

[Coanda]

1 hour ago, ToughButterCup said:

Drop in at my place and check mine over when yer driving south on the M6 from Cairn Ryan .... Are those numbers  (or rather the differences between them) what you'd expect?

I don't travel the M6 very often, so much as I'd like to I probably won't get to see yours.

 

I was hoping someone would comment on the numbers or more importantly, as you say the difference between them.

I'm not totally dissatisfied as the extract ducting is laying on top of the insulation and I know that temp will improve once covered and give a little more heat to be recovered. 

 

But I don't think that will make any difference to the basic efficiency of the exchanger.

[Coanda]

1 hour ago, JohnMo said:

So is this MVHR unit you made yourself?

 

What are the temperature sensors you used?

I bought a core cheap on a well known online auction site and made a polystyrene housing for it and a couple of inline fans which I had removed from extractors in the house. I then bought a batch of ducting, connectors etc from BPC and jerry rigged the whole thing up as a test.

The ducting, etc is all good and will be staying, I just need to decide if the unit is good enough, needs improving or replacing. 

 

The temperature sensors are not exactly state of the art but will give an indication.

 

Thlevel 4x Digital LCD Thermometer Temperature Monitor with External Probe for Fridge Freezer Refrigerator Aquarium (4x Black) : Amazon.co.uk: Large Appliances

[MJNewton]

2 hours ago, Coanda said:

 

I was hoping someone would comment on the numbers or more importantly, as you say the difference between them.

The labels are a little confusing, but I think I can work them out by their relative values. 

 

One way of calculating efficiency of the heat exchanger (although it's not perfect as a poorly insulated unit will result in higher figures if it allows heat from the room in) is simply:

 

( Supply - Intake ) / ( Extract - Intake )

 

Thus, with your figures:

 

( 15.0 - 12.8 ) / ( 16.7 - 12.8 ) = 0.56

 

56% efficiency isn't great given that >90% is readily achievable with off-the-shelf systems but I'd say it seems pretty good for something homemade though - it's certainly working! 

 

Edited November 19, 2023 by MJNewton

[Coanda]

I had hoped some wise person  would have commented on the efficiency or lack there of. So in the absence of that I searched for a formula online.

I found a formula for a PHI test. My house is nowhere near a PH but I applied the formula which gives 74%

 

Now that the temp outside has lowered it gives a rating of 80.7% not to shabby considering it's held together with titebond and duct tape.

 

The formula used is extract air minus exhaust over extract air minus intake.

Edited November 19, 2023 by Coanda

[Coanda]

8 minutes ago, MJNewton said:

The labels are a little confusing, but I think I can work them out by their relative values. 

 

One way of calculating efficiency of the heat exchanger (although it's not perfect as a poorly insulated unit will result in higher figures if it allows heat from the room in) is simply:

 

( Supply - Intake ) / ( Extract - Intake )

 

Thus, with your figures:

 

( 15.0 - 12.8 ) / ( 16.7 - 12.8 ) = 0.56

 

56% efficiency isn't great given that >90% is readily achievable with off-the-shelf heat exchangers but I'd say it seems pretty good for something homemade though - it's certainly working! 

 

Thank you for your reply.

Looks like we were posting at the same time.

 

One of the bits I read said about the heat from the room having an effect so although in my case it wouldn't matter cause it's in the cold attic space I didn't use it and opted for the passive house one.

[MJNewton]

8 minutes ago, Coanda said:

One of the bits I read said about the heat from the room having an effect so although in my case it wouldn't matter cause it's in the cold attic space I didn't use it and opted for the passive house one.

Yeah, if the unit is in a warm room then the supply-referenced calculation can result in apparent higher efficiency figures because the heat from the room warms a poorly insulated unit up and thus in turn creates a higher supply temperature too. With yours being in the attic though you won't be picking up that 'extra' heat if the ambient temoertaure is closer to the that of the intake. Internal thermal bridges will still lead to differences in results against an extract-based calculation to though. An average of both methods is arguably the best overall approach if you're after a single figure. 

Edited November 19, 2023 by MJNewton

[Coanda]

There's a problem, though I don't know how serious it is. Certainly not life threatening at this stage.

 

The fans I am using are not equally matched intake pushes through about 20% more than extract, so I'm going to, at some point have to replace one or both.

 

Where does one locate suitable fans, they don't come up in google searches.

[Russdl]

Whenever I’ve checked, our MVHR is supplying more than it extracts - not 20% though - so the house is always mildly over pressure which I presume is the way it should be* so don’t balance the fans too much. 
 

(*standing by to be corrected)

[MJNewton]

21 minutes ago, Coanda said:

Where does one locate suitable fans, they don't come up in google searches.

 

They are usually centrifugal EC fans which tend to be manufactured as OEM for inclusion into other supplier's products and so aren't quite so readily available directly to end users. They can be found though (examples) but there are a whole bunch of design parameters you'd need to know to narrow the search down e.g. airflow, noise, size, control etc.

Edited November 19, 2023 by MJNewton

[ToughButterCup]

Might be a useful idea to log those temperatures over (say) a year and post them here.

 

I'm really interested in the detailed design of what you did because we're fairly close to second fitting an MVHR system, but as usual don't have enough money.

 

Do any manufacturers  publish expected differences between the intake and outlet temperatures? Perhaps they might also do the same about the difference in expected relative humidity? 

 

Anyway, have you got any photographs of your self built unit? Don't be shy now...

[Coanda]

29 minutes ago, ToughButterCup said:

Might be a useful idea to log those temperatures over (say) a year and post them here.

It would but I doubt I could be dedicated enough, unless I could automate a system.

29 minutes ago, ToughButterCup said:

I'm really interested in the detailed design of what you did because we're fairly close to second fitting an MVHR system, but as usual don't have enough money.

 

Here's a couple of pics I took when I was building it. I built it big on the idea that the longer the air was inside the better. That may or may not be true. It's 820 by 800 by just under 500. It could have been quite a bit smaller and possibly worked as well. 

I made the enclosure from 50mm polystyrene. I wouldn't do that again. The polystyrene is cheap, light and easy to cut but born out of wedlock to glue.

After I've monitored and or tweaked it a bit I may make the box again from something more substantial. I'd like some suggestions, maybe MDF or good quality plywood.

 

29 minutes ago, ToughButterCup said:

Do any manufacturers  publish expected differences between the intake and outlet temperatures? Perhaps they might also do the same about the difference in expected relative humidity? 

Not that I've seen but I'm a newbie

29 minutes ago, ToughButterCup said:

 

Anyway, have you got any photographs of your self built unit? Don't be shy now...

Here you go.

[SteamyTea]

I just done a quick spreadsheet and, after rounding, shows your unit delivering 50%.

That is just on temperature and does not include enthalpy and moisture heat recovery.

[Marvin]

Monitoring our MVHR results, with the inlet and outlet ducts and MVHR in our loft, we soon realised that the results were seriously effected by the loft temperature.    We then super insulated the ducts and MVHR (2 to 300mm insulation to all) and we now have very good results in the high 80%. retained room temperature when using "heat recovery" (which also acts as cool recovery in the summer).

 

Good luck

 

M

  

[JohnMo]

Looks good, but the heat exchanger looks very small.

 

How about using individual extract fans say Greenwood dMEV, let them feed to the heat exchanger. The fans come with built in humidity sensors, are fully user adjustable. Then just run the supply at fixed speed. For the short period of boost in a single room, unbalancing isn't really much of an issue.

[SteamyTea]

All the temperature differences are very small as well.

You get a greater energy transfer when the deltas are greater.

 

 

[JohnMo]

26 minutes ago, Coanda said:

After I've monitored and or tweaked it a bit I may make the box again from something more substantial.

Make from a higher density EPS or XPS, mine are just XPS in a metal casing.

 

MDF laminated with EPS, to give some mechanical strength.

 

Other issue is filters unless you have the external to the unit.

[MJNewton]

31 minutes ago, Coanda said:

 

It looks great. and very neat! The sort of thing deserving of a perspex lid and internal lights... 😆

 

As mentioned above though it does seem rather on the small side, or am I being tricked by the perspective? Maximising contact time in the HEX is what's important; it doesn't matter how big the unit itself is. You will likely find that as your air flows increase the efficiency will drop - there's only a certain amount of transfer capacity available. You mentioned about sourcing fans; what are you using at the moment and are they representative flow-wise of what you are ultimately seeking?

[ToughButterCup]

Now that, that's interesting.

• .... unless I could automate a system

I invested in four or five SensorPush data loggers. Work on bluetooth, log every few seconds, and while not cheap, they are cheap enough for me to buy some. Mine ran for four years before the battery failed. Still working 6 years later. The output is easily understandable and can be sucked into a spreadsheet with ease.

Here's a quick look at a years' data.....

 

 

• suggestions for 'box' construction 

Dunno. But I know who will have an idea  : @Onoff @SteamyTea, @MikeSharp01, @Jeremy Harris , @TerryE, @JohnMo and especially @MJNewton

 

• You bought a core cheap (FleaBay)  

Can you explain what a 'core' is - yes it's a heat exchanger - ..... but what's the search term I should use so I can while away the long winter nights fantasizing about doing the same as you have.....

 

There's just one niggly naggly thing in the back of my mind......

The Apex DIYMAX man himself , @Jeremy Harris built all sorts of things on his MVHR installation ( he's likely building a nuclear reactor out of matchsticks somewhere right now).  But four years after he had finished his install,  he wrote about how he wished he had bought off the shelf stuff - maintainability and spare parts was the issue.

 

FoockIt: the end result doesn't matter, it's the journey that counts, right?  😐

 

 

 

 

Edited November 20, 2023 by ToughButterCup

[SteamyTea]

7 minutes ago, ToughButterCup said:

suggestions for 'box' construction 

Sheet insulation, polystyrene or PU.  Could be a secondary box stuffed with mineral wool.

8 minutes ago, ToughButterCup said:

Can you explain what a 'core' is - yes it's a heat exchanger

I think it is a general term for the heat exchanger itself, rather than the complete unit.

[ToughButterCup]

28 minutes ago, SteamyTea said:

...

That is just on temperature and does not include enthalpy and moisture heat recovery.

 

'... enthelapy and moisture heat ....'

I know its early on a Monday, but its in at the deep end - for me anyway. Given that Tinternet is full of shared ignorance, could you point me to something authoritative 1I can read up on enthelapy, and moisture heat please?

[SteamyTea]

1 minute ago, ToughButterCup said:

enthelapy and moisture

https://www.engineeringtoolbox.com/heat-recovery-efficiency-d_201.html

 

https://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.html

 

18 minutes ago, ToughButterCup said:

The Apex DIYMAX man himself , @Jeremy Harris built all sorts of things on his MVHR installation

He had MVHR unit with a heat pump in it as far as I know, and off the shelf unit, cant remember who made it now,