My HRV design

angstrom · 01-28-14, 01:36 AM

Hello Ecorenovators, I'm new to this forum and it's my first post.

I'm reading this forum for a while, was looking for ideas for my HRV project.
But finally ended up with my own design, as I'm a bit sceptical about using plastic for heat exchanger.
My inspiration for HRV is ecorenovator's forum, so I wanted to share with you what I came up with.
The heat exchanger is made from 0,5mm aluminium sheets, 1 meter x 0,33 meter. It's around 13 square meters of usefull surface area. Spacers between sheets are made from sheet rubber, 1 cm width, 4mm thick. One usually used for gaskets.
HRV housing is made from moisture resistant medium density fibreboard. Every inner corner is sealed with silicone.
In pictures you can see two white fans, it's simple, AC type, 70 W each, plastic housing fans with affordable price tag. I decided to mount them outside HRV housing as it is too big to fit inside.
As controls for unit I temporary use two speed regulators for fans and a simple timer. It turns on and off my HRV few times a day. As I said it's temporary, I really really wanted to test how my unit is performing.
And finally, performance. A few days ago it was -16 degrees C outside, and I got +8 degrees C air blowing into my living room and it the result AT FULL POWER. So, I'm quite happy. I'm planning to measure all four IN and OUT temperatures soon and calculate COP. If I only find a formula for it...
And I have a few questions for you guys.
How should I set the fans to work, a slight pressure or vacuum in house is better? As it's hard to make neutral.
I'm thinking in making some electronics with PWM and differential pressure sensor to control the fans work. But is it worth doing it? To have a moisture sensor in house would be nice too.

Daox · 01-28-14, 08:48 AM

Welcome to the posting side of the site angstrom! Its great to see lurkers post.

That looks like a very nice design. I'm sure some of the guys will have some more tips for you.

mrd · 01-28-14, 08:48 AM

With cold outdoor temperatures, a slight vacuum in the house is better. Your warm indoor air holds more moisture per volume, so if pressurized you'd have greater potential for in-wall condensation.

HRV performance figure calculations: Heat Recovery Efficiency

According to this, 0.5mm is about .020", 25 gauge. Are these sheets expensive? I've never priced aluminum sheet. How many layers do you have there?

From the photos, it appears to be a high quality build! Very nice work. I'm interested to hear your efficiency numbers.

angstrom · 01-29-14, 03:01 AM

Yesterday I did some additional performance testing. And according to the calculation tool here is the results. At full fan power (fan specification says 700 m3/h) COP is 59%, at half power - COP 69%. So I happily left it running at half power...
This result satisfy my expectations, I only invested 1/4 of a factory-made HRV price

I think I could improve COP by somehow improving air distribution between each layer. I suspect that majority of air is traveling through middle part of the core. Maybe by adding air filter in the chamber where air enters core...
The cost for aluminium sheets was ~100 USD. From these sheets I got 40-45 layers seen in photos.

kostas · 01-29-14, 02:45 PM

Excellent work! I guess that at -16 degrees incoming air will almost certainly make some dew, have you placed a collecting plate?

AC_Hacker · 01-29-14, 03:23 PM

Good job, good photos, respectable efficiency.

It looks like your HRV is counter flow... it's a little hard to tell from the photos. Is counterflow correct?

Where I live, the moisture is pretty high and condensation is always a problem.

Are you running into any condensation problems?

Great post.

-AC

angstrom · 01-30-14, 03:41 AM

My HRV is counter-flow. Only because this type of HRV tend to be more efficient.

In core, fresh air is coming from one end, "polluted" air is coming from another, so I think it's right.

Sure there is some condensation, you can see it in photo, but I simply drilled 2 mm hole for drainage. It doesn't have any effect on performance.

01-28-14, 01:36 AM	#1
angstrom Lurking Renovator Join Date: Jan 2014 Location: Vilnius, Lithuania Posts: 3 Thanks: 0 Thanked 0 Times in 0 Posts	My HRV design Hello Ecorenovators, I'm new to this forum and it's my first post. I'm reading this forum for a while, was looking for ideas for my HRV project. But finally ended up with my own design, as I'm a bit sceptical about using plastic for heat exchanger. My inspiration for HRV is ecorenovator's forum, so I wanted to share with you what I came up with. The heat exchanger is made from 0,5mm aluminium sheets, 1 meter x 0,33 meter. It's around 13 square meters of usefull surface area. Spacers between sheets are made from sheet rubber, 1 cm width, 4mm thick. One usually used for gaskets. HRV housing is made from moisture resistant medium density fibreboard. Every inner corner is sealed with silicone. In pictures you can see two white fans, it's simple, AC type, 70 W each, plastic housing fans with affordable price tag. I decided to mount them outside HRV housing as it is too big to fit inside. As controls for unit I temporary use two speed regulators for fans and a simple timer. It turns on and off my HRV few times a day. As I said it's temporary, I really really wanted to test how my unit is performing. And finally, performance. A few days ago it was -16 degrees C outside, and I got +8 degrees C air blowing into my living room and it the result AT FULL POWER. So, I'm quite happy. I'm planning to measure all four IN and OUT temperatures soon and calculate COP. If I only find a formula for it... And I have a few questions for you guys. How should I set the fans to work, a slight pressure or vacuum in house is better? As it's hard to make neutral. I'm thinking in making some electronics with PWM and differential pressure sensor to control the fans work. But is it worth doing it? To have a moisture sensor in house would be nice too. Attached Thumbnails Last edited by Daox; 01-28-14 at 08:44 AM..

01-28-14, 08:48 AM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Welcome to the posting side of the site angstrom! Its great to see lurkers post. That looks like a very nice design. I'm sure some of the guys will have some more tips for you. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

01-29-14, 03:23 PM	#6
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 724 Times in 534 Posts	Good job, good photos, respectable efficiency. It looks like your HRV is counter flow... it's a little hard to tell from the photos. Is counterflow correct? Where I live, the moisture is pretty high and condensation is always a problem. Are you running into any condensation problems? Great post. -AC __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...

01-30-14, 03:41 AM	#7
angstrom Lurking Renovator Join Date: Jan 2014 Location: Vilnius, Lithuania Posts: 3 Thanks: 0 Thanked 0 Times in 0 Posts	My HRV is counter-flow. Only because this type of HRV tend to be more efficient. In core, fresh air is coming from one end, "polluted" air is coming from another, so I think it's right. Sure there is some condensation, you can see it in photo, but I simply drilled 2 mm hole for drainage. It doesn't have any effect on performance. Attached Thumbnails Last edited by Daox; 01-30-14 at 10:00 AM..

01-28-14, 08:48 AM	#3
mrd Apprentice EcoRenovator Join Date: Feb 2010 Location: Milford, DE Posts: 106 Thanks: 5 Thanked 9 Times in 9 Posts	With cold outdoor temperatures, a slight vacuum in the house is better. Your warm indoor air holds more moisture per volume, so if pressurized you'd have greater potential for in-wall condensation. HRV performance figure calculations: Heat Recovery Efficiency According to this, 0.5mm is about .020", 25 gauge. Are these sheets expensive? I've never priced aluminum sheet. How many layers do you have there? From the photos, it appears to be a high quality build! Very nice work. I'm interested to hear your efficiency numbers.

01-29-14, 03:01 AM	#4
angstrom Lurking Renovator Join Date: Jan 2014 Location: Vilnius, Lithuania Posts: 3 Thanks: 0 Thanked 0 Times in 0 Posts	Yesterday I did some additional performance testing. And according to the calculation tool here is the results. At full fan power (fan specification says 700 m3/h) COP is 59%, at half power - COP 69%. So I happily left it running at half power... This result satisfy my expectations, I only invested 1/4 of a factory-made HRV price I think I could improve COP by somehow improving air distribution between each layer. I suspect that majority of air is traveling through middle part of the core. Maybe by adding air filter in the chamber where air enters core... The cost for aluminium sheets was ~100 USD. From these sheets I got 40-45 layers seen in photos.

01-29-14, 02:45 PM	#5
kostas Helper EcoRenovator Join Date: Dec 2012 Location: Venice, Italy Posts: 89 Thanks: 15 Thanked 41 Times in 19 Posts	Excellent work! I guess that at -16 degrees incoming air will almost certainly make some dew, have you placed a collecting plate?