Up and running

[JohnMo]

32 minutes ago, ToughButterCup said:

invested in four or five SensorPush data loggers

Or Shelly H&T, currently 40% off, at Shelly store, similar output. Not sure how you get data to excel though.

 

[Onoff]

https://www.builditsolar.com/Experimental/DIYHRV/DIYHRV.htm

[Coanda]

1 hour ago, SteamyTea said:

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.

May I enquire what formula you used?

[Coanda]

1 hour ago, JohnMo said:

Looks good, but the heat exchanger looks very small.

The exchanger/core is 227 by 227 by 383.

1 hour ago, JohnMo said:

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.

I looked those fans up, they look like a possible solution, Do you happen to know what their flow rate is?

[Coanda]

1 hour ago, SteamyTea said:

All the temperature differences are very small as well.

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

 

 

I get that. But I'm old school, I heat all of my house to 15/16 deg which is comfortable for the bedroom and kitchen and enough to keep unused rooms from going stale. The living room has a wood burner which keeps me cosy in the evenings.

[Coanda]

1 hour ago, JohnMo said:

MDF laminated with EPS, to give some mechanical strength.

Yeah, thinking along those lines

1 hour ago, JohnMo said:

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

None at present but carbon on way from Temu.

[Coanda]

1 hour ago, MJNewton said:

 

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

Like my wheelie bin vacuum.   I put a perspex lid on it and now I can be mesmerised by the saw dust swirling round and round and,,,,

1 hour ago, MJNewton said:

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.

It's 227 by 227 by 383 on the small side I would agree but I may manufacture a second one from corriboard and put them in series.

 

1 hour ago, MJNewton said:

 

You mentioned about sourcing fans; what are you using at the moment and are they representative flow-wise of what you are ultimately seeking?

Fans are definitely a problem, although I am looking into ones recommended earlier by Johnmo.

The two I am using now are repurposed inline fans, one Monrose and another similar. They are rated <> 180- 230 M3h but they are not doing that and they are not balanced,

I only have one duct going to each Plenum, I'm wondering would two allow more air with the same fan speed or would better fans be a better bet.

[SteamyTea]

16 minutes ago, Coanda said:

I get that. But I'm old school, I heat all of my house to 15/16 deg which is comfortable for the bedroom and kitchen and enough to keep unused rooms from going stale. The living room has a wood burner which keeps me cosy in the evenings.

You may find that as the temperature difference increased, so does the efficiency.

 

The energy usage of the fans needs to be subtracted from the total.

Small fans are inefficient, so the largest fan you can get away with is best.

Have to be careful if using a speed controller as some can use quite a bit of energy on their own, though that can be put into the room outlets.

[JohnMo]

21 minutes ago, Coanda said:

The exchanger/core is 227 by 227 by 383.

I looked those fans up, they look like a possible solution, Do you happen to know what their flow rate is?

Range is 2 to 23 l/s. I have one set about 4 - you have to take the cover of to check it running as it is completely silent.

CV2-GIP.pdf

[Coanda]

1 hour ago, ToughButterCup said:

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.

Velly intellesting.

1 hour ago, ToughButterCup said:

 

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.....

I searched for mvhr core. There doesn't appear to be any great bargains at present but keep looking, I did,

 

1 hour ago, ToughButterCup said:

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.

If he had bought it off the shelf, four years later he would have wished he made it himself or something else, such is human nature.

1 hour ago, ToughButterCup said:

 

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

Yes I agree, I'm retired with time on my hands, a small workshop and a reasonable amount of tools so why not have a go.

At the same time if I found a complete unit for a knock down price I would buy it and pass my time some other way.  

[SteamyTea]

2 hours ago, Coanda said:

May I enquire what formula you used?

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

[Coanda]

20 hours ago, JohnMo said:

Range is 2 to 23 l/s. I have one set about 4 - you have to take the cover of to check it running as it is completely silent.

CV2-GIP.pdf 391.93 kB · 1 download

Are you using it on it's own or part of a mvhr set up?

[JohnMo]

23 minutes ago, Coanda said:

Are you using it on it's own or part of a mvhr set up?

It's in our summer house, which the wife uses for Reiki etc. so has to be quite. Had another make of dMEV fan in originally but it was too noisy.

[Coanda]

Very pleased with my set up today.

The numbers are.

intake  12.1c

exhaust  10.6c

supply to house  13.4c

extract from house 14.4c

Sun is shining on the back of the house where the intake is.

That has to be a good percentage no matter how you count it.

[MJNewton]

7 minutes ago, Coanda said:

That has to be a good percentage no matter how you count it.

 

Forgive me sounding so negative but if you take the simple ( Supply - Intake ) / ( Extract - Intake ) calculation method that gives ( 13.4 - 12.1 ) / ( 14.4 - 12.1 ) = 57% which isn't all that high? Better than 0% of course so heat is being recovered, but it's not really in the ball park (85%+) that is realistically achievable with these units.

[Coanda]

11 minutes ago, MJNewton said:

 

Forgive me sounding so negative but if you take the simple ( Supply - Intake ) / ( Extract - Intake ) calculation method that gives ( 13.4 - 12.1 ) / ( 14.4 - 12.1 ) = 57% which isn't all that high? Better than 0% of course so heat is being recovered, but it's not really in the ball park (85%+) that is realistically achievable with these units.

Thank you for pointing that out, no point deluding myself. I wrongly figured because the intake was warmer than the exhaust, it had to be good.

 

[MJNewton]

31 minutes ago, Coanda said:

I wrongly figured because the intake was warmer than the exhaust, it had to be good.

 

I was going to comment on that actually as I am not quite sure how that has happened. The temperature sensors haven't been swapped round have they?

[Coanda]

57 minutes ago, MJNewton said:

 

I was going to comment on that actually as I am not quite sure how that has happened. The temperature sensors haven't been swapped round have they?

Nothing has been changed, it's just that it's a lovely sunny day here and the intake is on the south facing roof side.

I've been reading here to try and get my head round this % thing.

Cheap MVHR or expensive MVHR? The science behind Heat Exchanger Efficiency - Heat, Space and Light Ltd (heatspaceandlight.com)

 

Why different methods. I mean 2 and 2 is 4 but apparently not in this case.

[MJNewton]

1 hour ago, Coanda said:

Why different methods. I mean 2 and 2 is 4 but apparently not in this case.

 

If the calculation focuses on how much the supply temperature has risen it doesn't consider where the source of that heat comes from, or rather assumes it is all from heat transferred from the extracted air. The reality is that some heat may have come from the air surrounding the box itself, the contribution of which will be greater with a poorly insulated unit than a well insulated one. Similarly with one that leaks air compared to one that is airtight. Hence poor units get 'rewarded' (as in appear better) than better ones using such a calculation.

 

If you take an alternative approach that isn't based on supply temperature but factors in exhaust temperature (i.e. it views the unit from the opposite direction in terms of heat transfer), then that same heat leakage that artificially increases the supply temperature is picked up by the increase in exhaust temperature and results in a decrease in calculated efficiency. Thus poor units now get 'punished' for any leakage that exists.

[Coanda]

Have i got this right.

Using todays figures

13.4-12.1=1.3.   14.4-12.1= 2.3.    1.3/2.3= 56.5%

 

 

 

14.4-10.6=3.8   14.4-12.1= 2.3        3.8/2.3=165.2%

 

Hellova difference.

[MJNewton]

19 minutes ago, Coanda said:

Hellova difference.

 

Yeah, and suggests there's something wrong with the figures (or something external that is skewing them).

[JohnMo]

I purchased the same gauges as yourself and had similar rubbish results.

 

The heat exchanger is designed to see equal flow on supply and extract, if it doesn't you get a bad efficiency result.

 

So I got out the flow meter and found the supply flow was set too high, I adjusted it and the room supply is now 4 to 5 degs warmer. Just looked at an hour later and extract and supply to rooms is within a degree.

 

 

[Coanda]

44 minutes ago, MJNewton said:

 

Yeah, and suggests there's something wrong with the figures (or something external that is skewing them).

What I think is skewing it is that intake temp is higher than exhaust because of the heat on the south facing roof.

 

If we take yesterdays figures of intake 0.4  exhaust 3, supply 7.9 and extract 10.6.

7.9-0.4=7.5  and 10.6-0.4=10.2.     7.5/10.2=73.5%  for SAP

and

10.6-3=7.6   and 10.6-0.4=10.2       7.6/10.2=74.5%

 

If the formula was correct you'd expect similar results over a range of readings. No?

[Coanda]

25 minutes ago, JohnMo said:

I purchased the same gauges as yourself and had similar rubbish results.

 

The heat exchanger is designed to see equal flow on supply and extract, if it doesn't you get a bad efficiency result.

 

So I got out the flow meter and found the supply flow was set too high, I adjusted it and the room supply is now 4 to 5 degs warmer. Just looked at an hour later and extract and supply to rooms is within a degree.

 

 

I know that my input exceeds the output by maybe 20% but I bought a speed controller for the faster fan. So that's a job for tomorrow.

But the formula doesn't know that input air is more than output so it's the same for both.

[JohnMo]

4 minutes ago, Coanda said:

I know that my input exceeds the output by maybe 20% but I bought a speed controller for the faster fan. So that's a job for tomorrow.

But the formula doesn't know that input air is more than output so it's the same for both.

20% more cold air will overwhelm the warm air coming out and therefore not heat the incoming air as much. Once you get that sorted you will see a good increase in efficiency.