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Would anyone like to critique my DIY heat exchanger?


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Playing on sketch up before I actually cut anything.

 

I saved a fortune already.:)

 

It's 800mm by 800mm and the ducts are 180mm 

 

The core is 227 by 227 by 383

 

MV1.jpg

MV2.jpg

Edited by Coanda
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What about the fans?

What about filters to keep the HE clean?

 

I only paid £250 for a new unit on eBay, so not sure you will be saving much but if it's project/hobby don't flag it as a money saver.

 

Would it be easier to have a square box with a heat exchanger at 45 deg, then the inlet outlets can be on a straight face instead of a lot of different angles?

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12 minutes ago, JohnMo said:

What about the fans?

What about filters to keep the HE clean?

I'm going to use two inline fans which I already have.

I believe filter material can be bought and cut to size.

 

12 minutes ago, JohnMo said:

 

I only paid £250 for a new unit on eBay, so not sure you will be saving much but if it's project/hobby don't flag it as a money saver.

Cheapest I saw, that I would consider, on ebay was over £600. If you don't mind what did you get for £350?

 

12 minutes ago, JohnMo said:

 

Would it be easier to have a square box with a heat exchanger at 45 deg, then the inlet outlets can be on a straight face instead of a lot of different angles?

I started off with an oblong box but miscalculated the amount of space I needed for the spigots. I may well go back to that.

 

Thank you for your comments

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9 minutes ago, ProDave said:

The frame is easy.  What about the actual heat exchanger, how are you making that?

My intention was to make it with corriboard by I stumbled upon one of these brand new in box for seriously little money, it just didn't make sense to waste time and material making it.

 

Daikin 110635J HEAT EXCHANGE ELEMENT 227x227x383 (climatecontrolsandspares.co.uk)

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6 minutes ago, Coanda said:

I'm going to use two inline fans which I already have.

Generally speaking, the physically smaller a fan is, the less efficient it is.

I used 2 Manrose remote bathroom fans on my DIY MVHR.  I think they used more energy than they saved.

Ideally you want large fans, running at a slow speed.

Remember that 1 watt is the ability to move 1 kg, 1 meter, every second.  Now a kg of air is 0.8 m2, a 1 W fan is not going to do that as the efficiency is probably around 5%.

Edited by SteamyTea
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57 minutes ago, SteamyTea said:

Generally speaking, the physically smaller a fan is, the less efficient it is.

I used 2 Manrose remote bathroom fans on my DIY MVHR.  I think they used more energy than they saved.

Ideally you want large fans, running at a slow speed.

One of mine is a Manrose and the other looks and acts just like it.

If I remember correctly one says 250 m3H but at present it's way out of easy access in the roof space.

 

My plan is to rig this up to see what effect it has and I'm not going to spend unnecessarily until I'm sure of the benefits. Then I can either improve this. most likely. or spend some dosh, not as likely but definitely a possibly.

 

57 minutes ago, SteamyTea said:

Remember that 1 watt is the ability to move 1 kg, 1 meter, every second.  Now a kg of air is 0.8 m2, a 1 W fan is not going to do that as the efficiency is probably around 5%.

I think they're rated a 30 or 40 watts so not going to break the bank for a month or two.

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1 hour ago, Russdl said:

@Coanda (you got me at ‘SketchUp’ love it!)

 

What do you plan on building the frame out of?

 

50mm polystyrene.

1 hour ago, Russdl said:

Any plan for a summer bypass?

I live in Co Antrim, we don't get summers. :)

Seriously I do have lots of ideas about Co2 sensors etc, but not for a while, need to get it working first.

I'd be delighted if I needed a summer bypass but at best it would be only required 2 or three weeks a year.

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37 minutes ago, Coanda said:

250 m3H

0.0694 m3/s or 0.0556 kg/s

41 minutes ago, Coanda said:

I think they're rated a 30 or 40 watts

At 30 W, that makes the efficiency 0.23%, I was miles out (and I got a 2 instead of a 3 for the volume).

 

43 minutes ago, Coanda said:

My plan is to rig this up to see what effect it has and I'm not going to spend unnecessarily until I'm sure of the benefits.

Yes, just do it as it is great fun.  Mine did recover quite a bit of energy, but not the amount the fans used.

But you can go looking for better fans and plumb them it later.

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1 hour ago, SteamyTea said:

0.0694 m3/s or 0.0556 kg/s

Sorry, can you elaborate, I'm not getting that.

 

Edit to say I got it now, 

1 hour ago, SteamyTea said:

Yes, just do it as it is great fun.  Mine did recover quite a bit of energy, but not the amount the fans used.

But you can go looking for better fans and plumb them it later.

Yes that's the plan but any recovery I make is profit since the fans are running anyway to ventilate the place.

They've been running 24/7 for the last couple of weeks and I think the RF may be dropping a little, but maybe not because of the fans.

Edited by Coanda
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2 minutes ago, Coanda said:

Just for interest, do you have any recommendations, for when the time comes?

No.

It is partly why I stalled on the DIY solution.

 

I do have an idea about using large car radiators connected in a thermosyphon configuration.

They come with fans that can be easily controlled, have a very large transfer area, are already rectangular, so easy to box in, can fit though a loft hatch. 

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4 minutes ago, SteamyTea said:

No.

It is partly why I stalled on the DIY solution.

 

I do have an idea about using large car radiators connected in a thermosyphon configuration.

They come with fans that can be easily controlled, have a very large transfer area, are already rectangular, so easy to box in, can fit though a loft hatch. 

Interesting idea!  I think you’d need lots of them- if you had just one pair, and one thermosiphon, then I think the theoretical best efficiency will be 50%.   
 

Often mvhr have hexagon shaped cores (well ours does), so that a lot of the heat exchanger is counter flow rather than cross flow, as this improves efficiency - like the pic below.  The HX is best made with many sheets of thin plastic spaced a couple of mm apart, more total area gives better efficiency.

 

CO2 controlled fans are a massive efficiency improvement - you could do this with/without the HX.  There are simple ones with 0-10V o/p available from digikey.  
IMG_0161.thumb.jpeg.1b6d62372106d3af316faada1b8d0329.jpeg

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1 minute ago, RobLe said:

Interesting idea!  I think you’d need lots of them- if you had just one pair, and one thermosiphon, then I think the theoretical best efficiency will be 50%.

I have not calculated it, was just an idea when I saw two Transit Van radiators against a wall at the garage that MOTed my car.

Why we need is a pikey that owns a scrapyard as a member then they can get us all sorts of bits to try out.

 

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IMG_20231102_144830_480.thumb.jpg.5fdf02b19c79dbd6e883ed1867074f97.jpgIMG_20231102_144821_480.thumb.jpg.a67f519140c33a52010fa02aba2481ca.jpgI spent some time this afternoon cutting the parts. Careful design means I get it all out of one sheet of polystyrene. Overall size is 800mm by 820. by 485.

I've glued up a couple of test pieces with no more nails, and if its a success, I'll do the rest tomorrow.

I'm wondering should I use dowels for added strength?

 

 

 

 

Edited by Coanda
Pics didn't attach
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Are you going to put a temperature/RH logger on it, maybe one of my cheap energy meters as well.

Should cost about 40 quids all in.

 

Airflow would be a bit harder to do, something I keep meaning to look at.

Edited by SteamyTea
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On 31/10/2023 at 17:38, Coanda said:

Playing on sketch up before I actually cut anything.

 

I saved a fortune already.:)

 

It's 800mm by 800mm and the ducts are 180mm 

 

The core is 227 by 227 by 383

 

MV1.jpg

MV2.jpg

That's a crossflow design I'd say. And therfore less efficient. 

 

As @RobLe pointed out you really want to start with a counterflow design. 

 

It makes a very big difference to efficiency.

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35 minutes ago, SteamyTea said:

Are you going to put a temperature/RH logger on it, maybe one of my cheap energy meters as well.

Should cost about 40 quids all in.

 

Airflow would be a bit harder to do, something I keep meaning to look at.

I'd be really interested in that.

 

Fill me in.

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17 minutes ago, Miek said:

That's a crossflow design I'd say. And therfore less efficient. 

 

As @RobLe pointed out you really want to start with a counterflow design. 

 

It makes a very big difference to efficiency.

I can't disagree.

But this is my first attempt, which I am treating as a learning curve. 

 

Using what I have as far as possible and the crossflow core which didn't cost much at all.

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59 minutes ago, Coanda said:

Fill me in.

Which bit you interested in?

 

Basically you can buy the cheapest Raspberry Pi Zero W, 4 DHT22 sensors, a light dependant diode and a cheap electrical meter with a pulse LED on it, wire them up and log the data to a file.

 

I have know idea if you have any coding/Linux experience, but it is really quite simple to set something like this up with instructions.  A few quirts to overcome, but basic stuff.

 

Here is a bit about the energy meter.

 

Edited by SteamyTea
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