Hi All,

It's been a while since I posted but there are so many details that it would be a very long post.

So instead I'll start with a simple write-up summing up some of my experiences so far, not very organized. A great chance for you all to ask about points of interest on which I can give details.

I 'fired up the engines' on january 9th when I got all the ducts more or less connected so I had the airflows. Back then none of the ducts were insulated so a lot of heat was exchanged with the surroundings (the unheated shed).

I kept the apparatus running since, aside of short intervals when I needed to disconnect ducts or disassemble the HX-core. Since 'launch' I properly routed all ducts and insulated them, also applied dustfilters.

- Since starting the HRV the windows stayed closed, which greatly increased comfort in the livingroom since the lowest 2 feet weren't so cold anymore.
- We did turn on the heating higher than in previous winters (ohh, bad).
- We used around 15% less NG on heating than in 2012 calculated on heating degree days, even with the heating set to higher temperatures.
- With the central heating running less the rooms upstairs were noticably colder.

- Old Air Out is drawn out from the kitchen, right underneath the ceiling. Here the temperature could reach 28C with 3 pans on the furnace while preparing food and as a result the Fresh Air Out (blowing fresh air into the livingroom) could reach a whopping 24C. As a result I turned down the thermostat half an hour before cooking, otherwise it would get way too warm in the livingroom :- )

- The Fresh Air In blowing air into the livingroom created a strong airflow sticking to the ceiling, untill reaching the opposite wall right above the couch. While sitting on that couch a noticable draught was felt. I modified the inlet to create a more diffuse airflow.

- With the larger amount of air ventilated the inside air feels much fresher and there appears to be less dust settling on furniture and such.

- I don't have good temperature measurements. I only have 2 simple thermometers on which I can guestimate values by half a centigrade. This makes calculating the efficiency of my HRV a bit tricky, especially since temperaturedifferences are quite small. Best I can say is that it's between 65 and 75%.
Yesterday I ordered a buch of digital thermometers from DealExtreme. Alas the weather is improving and the heatingseason is comming to an end, oh wait, that is a good thing!

- Designflaw: The square area of my filters as applied now is too small, clogs up relatively fast causing imballance between the 2 airflows.

- Designflaw: Negative pressure on both channels in the HX-Core. The core _will_ leak so it must be: draw stale air and push fresh air through the HX-Core. (Observeable while cooking, and you don't even need a lot of garlic.) That way the leaking will be from the fresh to the old air, so the incomming air to my livingroom will be 100% fresh.

So on my to-do list are:
- make seperate filterboxes.
- relocate the fan in the fresh air channel so it pushes air into the HX-Core.


I did make another modification to my HX-Core and I can say the fans I choose are working lovely. More on that later though.

Fornax

Hey, this is great news, Formax!
Today, as I was coming back from work, I was wondering what happened to this thread, and I was planning to give some info, too. So I guess you have beaten me on time ;)
As for me, I dismantled everything last week, now it's quite warm and I will soon need my balcony to be ready for having dinner outside, so I put everything back in my garage.
It's also good to hear that you are happy with the motors. Did you managed to get some current consumption data, too?

Heya Kostas,

As for the fans, yes I have some data. A few weeks back I connected them to my kill-a-watt so I can monitor their combined powerconsumption.

According to their specsheet in the lowest setting (of 3) they are said to use 8 watts. What I measure right now is 34 watts though for the two combined.
To me this is plausible since the fans have to overcome the load of the dustfilters and the HX-core. I can also see when the filter(s) are getting poluted, powerusage will climb up slightly to 36/37W.

Earlier I mentioned to you the fans are very silent. And indeed they are when they need not overcome any resistance. As they are now they do make some sound, comparable with any whole-house-ventilator.

To me this is not a problem, the fans are located in a different room and the sound through the ducting is only noticeable when you know what to listen to. (The HD in my mediaplayer is louder).

Together for both fans the use of electricity is about half of that of the single whole-house-fan that was installed 30 years ago, still a win-win situation.

Nearly 40w / 24h use (worst case) means aprox 1Kwh/day, that's almost €6/month, at least here in Italy. Not bad at all, a better living surely worth it!
Thanks for your feedback, Fornax ;)

Thanks for the data!
When you install larger filters the resistance should drop, and with it the noise and power consumption.

I aquired and installed 4 thermometers with good resolution so now I have somewhat reliable numbers on how my HRV performs.

The thermometers I got are discussed here

It turns out my HX-core is not as efficient as I expected/hoped it to be. A good thing though is that my FAI (Fresh Air In) is preheated for free by my crawlspace so the low efficiency of the HX-core didn't leave me with cold fresh air when it was freezing 15 degrees centigrade last winter : ) The lowest FAI I measured back then was around +12C.

These measurements are taken when the system had been in a steady state for a while (Central heating off, no cooking, no direct sun in the kitchen).
Values are also adjusted from the raw readings to the actual temperatures, oh, in degrees celcius.

One can see the calculated efficiency is quite consistent.. and low. Only 66% where one would expect a counterflow HX to perform better than this.
Also IN and OUT are the same which means both flows appear to be balanced nicely. I asume this indicates that my fans are working fine and I made the right guesses when choosing diameter of ducting.

So I have a working HRV that even my wife is appreciating by now. Now I need to think about what is wrong with the HX-core and how to improve it using what I have. I have some ideas but no rush, heatingseason is over.

Fornax

Testing post for the first time.

Commercial or DIY HRV for a cottage in California?
 

OK, my test worked so here goes...

Greetings everyone! I'm a new member and I think it took me four hours to go through all of the posts going back more than three years! I commend and thank all of you for keeping the conversation going for so long with such camraderie and enthusiasm.

I have a few comments before I introduce my own situation with HRVs. First, if any of you who have successfully built working devices are interested, I encourage you to post detailed instructions on instructables.com, or some similar site, where many more people will be able to access them easily. Second, it would be great if someone compiled an "HRV lessons learned and great links" thread. The bottom line is that the vast amount of information in this thread is too dispersed and difficult to access, considering the digital age that we live in.

Regarding HRV designs, I don't have much to add to the conversation (at least not yet), but I did come across some materials that I don't think have been mentioned here. There are three different types of signage material similar to coroplast, but with aluminum on the exterior instead of plastic (the corrugated core is still plastic). These are called Alumalite, D-lite, and Econo-lite, Unfortunately, they are all rather pricey, but they would probably offer somewhat better heat exchange than coroplast.


My situation is the following: I live in Berkeley, CA and I have a 300 square foot cottage in my backyard that is a converted garage, and which I rent to a single person. The climate here is very mild and on the cool side, known for our foggy summer mornings. In the winter, the daily temperature generally goes from 4-13 C and in the summer from 13-22 C. The cottage is an uninsulated, concrete block building (except the roof is insulated), that has one large space with a kitchenette, and a small, separate bathroom. In its present state, the cottage is very inefficient in terms of heating (it's heated with a modern natural gas space heater).

I'm planning to add insulation and drywall to the West and North walls, and possibly make the South wall into a Trombe wall (it has very good solar exposure), put in double paned windows and add a layer of insulation and laminate flooring on the concrete slab. The cottage tends to be damp, especially in the rainy season, and that's why I want to put in an HRV. Since the space is only 300 square feet, I think the HRV only needs to have a flow rate of 20 cfm or so.

My quandry now is whether to buy a unit or go DIY. All of the commercial HVRs that I have come across are much too big for such a small space. Through this thread, I learned about the Panasonic WhisperComfort™ Spot ERV. It has a very low flow rate, low energy consumption and it's very reasonably priced. However, it is an ERV, so my concern is that it will not remove enough of the excess humidity that I want to get rid of. I spoke to a sales rep at Panasonic today, and he said that the Whispercomfort would only pull moisture out of the interior air when the humidity is higher indoors than outdoors. That sounds pretty good to me, but I'm not sure. Perhaps I should start by measuring the indoor and outdoor humidity over a period of time. Can any of you shed some light on this issue? Most of the info I've seen online, as well as in this thread, pertains to places with more extreme climates than what we have, so I need help conceptualizing how this ERV would perform in my situation. If I can get to a place of feeling like the Panasonic will do a good job, then I'll probably buy one. But, I don't want to make that investment and then find that the cottage is still too damp afterwards.

On the DIY side, I really like the results that some of you have gotten with your HVRs. My main two concerns are that I have so many other projects brewing that adding the HVR would be burdensome (I want to have a working HVR within six months). I also wonder whether a DIY HVR would be reliable in the long term. Also, I am not living in the cottage, and I don't want our tenant to be too much of a guinea pig, especially since ventilation does affect one's health. If I decide not to go DIY for the cottage, I still have the option of making one later for my clothes dryer exhaust (another great idea from this thread!) If I do go DIY for this project, I also wonder how to size the heat exchanger.

Thanks, in advance, for your advice!

WattWatcher,

Thanks for your post. I think your idea of a 'lessons learned' thread is one that is very much needed, and there's probably no one better suited for that project than you, since you recognized the need and have just read the entire thread.

It would be helpful to everyone if you took that on. As you can see, many people have done considerable research and also have done hands on work which they were so generous to document and share.

Your authorship of that thread would be would be a generous contribution on the very same scale.

Best of Luck,

-AC

Ventilation will keep indoor humidity down if the outdoor dew point temperature is at least 20 deg F lower than the inside temperature. For example, the outdoor dewpoint right now is 58 deg F at the Oakland airport. If the indoor temperature is below 78 deg F, the house will be humid inside. If the house is poorly ventilated, it will be even more humid inside.

If the outdoor dewpoint reaches 70 deg F, the house will be a swamp inside. The solution is a dehumidifier. No need for ductwork, just put it anywhere in the house and set it for about 50% RH.

I know nothing about dew point and humidity, but I have read that HVRs can make a damp interior drier. Obviously I have to educate myself about this topic. So, why would my house be drier, while the cottage is damp, since they both experience the same climate? Doesn't infiltration have something to do with that? Right now, the dewpoint in Berkeley is 56F and it's 68F in my house, but I don't think it's really humid in here. This is all very interesting!

I think the problem with dehumidifiers is that they use a lot of energy, like hundreds of watts.

Dew points getting above about 55 degrees is where things get a little too moist inside. 55 degrees is the point where if my house is at that point and the air conditioner hasn't run in the past 24 hours, I will have it run for 2 hours. I kept my house hot last summer and stayed in the lower levels so the indoor dewpoint and outdoor dew point got a chance to get above 55 degrees. We had dew points well over 70 degrees outside so it was very necessary to run the A/C on a daily basis around the June, July, August timeframe especially. Running the A/C for two hours brought the house down to a dew point under 50 degrees and it was comfortable at about that point. I basically set my thermostat for 2 of the coolest night hours as long as they were going to be above 60 degrees outside and that is the most efficient temperature that my A/C would run without any risk of freezing the coil and lines back to the condenser.

You might want to get one or two of these things.

I have one and it's been an amazing education. The thermometer is very accurate, as is the humidity sensor, and the instrument calculates the dew point, AND if your dew point coincides with temperatures that are conducive to mold growth, it will flash (and beep if you so desire).

-AC

We have a very different climate here in Berkeley, no need for air conditioning at all. I think that must mean that our dew point is usually below 60F, but I've only just started paying attention to that number. Right now, 10 PM, the dew point is 50F and the temperature is 59F. Most likely, the outdoor air will reach the dew point before the Sun comes up tomorrow. In my house, the temperature is 69F, but I don't know what the %RH is. Would be interesting to compare %RH in my house and in the cottage. Here's a question: are uninsulated concrete block structures damp because the cold walls and floor tend to condense moisture on their surfaces?

If a surface, any surface, has a temperature below the dew point of the air around that surface, there will be condensation on that surface. It does not matter if the surface is concrete, wood, or a cold bottle of beer.

Yes, that looks like a really great device. Thanks!

Found some interesting products from the U.K. The first two use the spiral/tubular heat exchanger that was mentioned in this thread at one point. The last one is really interesting - a passive HRV, apparently just going on the market in the U.K.

Retrovent by Envirovent
The RetroVent - Heat Recovery Extract Fan! - YouTube
HeatSava by Envirovent
heatSava Single Room Heat Recovery - YouTube
http://www.envirovent.com/downloads/...a_brochure.pdf

Ventive Passive HRV System
| Sustainability Workshop

I've decided to try building a heat exchanger core with the simple cross flow tube design. Below is a link to CAD model of the concept. I'm going to use polypropylene drinking straws for the tubes. They have a wall thickness of only .0055 inches (0.14mm). I'm still not sure how closely I will space the straws on my first attempt, but either way, it will be an experiment. I think I'm going to use this fan, which I found on Amazon Coolerguys 120x25mm Blower Fan 12v with 3pin Connector. It delivers 17 CFM and the specs say that it's very quiet (<20 dB)

Flickr: Drinking Straw HX

Hi All,

A while back I discovered that the HX-core in my HRV is not as efficient as I expected it to be and I found the cause. It comes down to the choice of material.

The plates are made of aluminium. Even worse, the plates are made of relatively thick aluminium, 1mm (1/25"). They conduct heat very well, which is a good thing when you want to transfer heat from one surface to the other surface. But heat will also spread out from any point on the plate throughout the plate in all directions.
That is a good thing if you are building a heatsink to cool a CPU and you want to transport the heat away.
In a heatexchanger you want to transport the heat on any given location only to the other side of the surface on that spot, you do not want to transfer the heat over the surface of the plate to another location.

Aluminium HX-cores are still a good idea if you can:
- make the material thin enough
- make the air move fast enough, say 5m/S
but now you need to:
- overcome pressure loss by using more powerfull fans
- higher airspeeds produce more noise, either live with that or deal with it in another way.

I have been playing with the calculator that can be downloaded from www.heatex.com and their HX-cores do the same, at lower airspeeds they are less efficient, reaching a maximum at a certain point and then declining again.

So what I would like is a heatexchanger build from some sort of plastic, but I find that hard to find in my neighbourhood, or else it is as expensive as aluminium.

And then I found the solution, see next post : )

...continued

Hi All,

I found a dutch company, Recair, that produces recuperators out of polystyrene.
Their heatexchangers are very efficient and of course they are counterflow. The internal design looks very good with triangular ducts, see this snippet taken from their productfolder.

http://ecorenovator.org/forum/member...ular-ducts.jpg

Their website, www.recair.nl, is available in multiple languages. It also has a nice online calculator to play with.
They do not sell their products to individuals but at this website, warmtewisselaarwebshop.nl, I can order them in the Netherlands, no idea about shipping to other countries. These recuperators are very reasonably priced!

So this summer, after some other projects around the house, I will be rebuilding my HRV with one of these heatexchangers inside. I'll probably use the RS160 with a height of 250 or 300mm.

Fornax

Intercooler
 

I stumbled across a turbocharger intercooler and said, "What the heck" and bought it for $5.
Plan is to stick it diagonally in the window so the ports
fall inside and outside the plane of the window. Been trying
to figger out how to make the air pass thru multiple times
to create something more like a cross-flow exchanger.
But it's so massive that it might not make much difference.

If I can figure out which car it fits, I might be better off selling
it and buying a real HRV.

Ideas?

Sell it man, use money for a better heat exchanger. I say this as a person that could use an intercooler.

Hi there, new guy here, great thread, lots of great stuff, anyone working on anything at this time??
I've just acquired a number or sheets of 4mm corrugated plastic (sign material) and am about to start hacking it up and stacking an HX... I see that the cross-flow approach is really simple to build, and I also see a lot of reference to counter-flow... (as in two cross-flow HXs "configured in a counter-flow configuration" I'm having a hard time understanding how 2x cross-flow = counter-flow... but that's anothe thing...) so I 'm wondering how others might have approached configuring sign material in a manner that the opposing air streams are in true counter flow configuration as opposed to 90* angle to each other... Descriptions would be nice, but I'm a visual person so a diagram or picture is worth a million words for me... Any help would be appreciated!

Hey, I have a substantial stack (1' x 1' x 1.5') of pre-cut pieces that you can have for free... I used them for experiments (which worked just fine) and have decided to use a different approach.

Washougal is close to Portland, right?

Do you want them?

-AC

yeah! I'll take em! I'm just about to head to Portland... how do we connect?

Send me a private message or email.

-AC

It's not letting me... not enough posts... email me if u can...

It was a pleasure meeting you today AC! Thanks again for the HX material! I'll keep the group posted on how it's put to use.

We'll need to get together again soon and conspire to save some energy! (Let me know if you got my email)

geodans, great to meet you, too.

I'm glad to be able to help you on your HRV project.

Your new home build sounded pretty spectacular from a EcoRenovator point of view. I don't know if you did much in the way of progress photos, as you went along, but if you did I, think they belong on a new thread. You may have established a new high water mark.

Yes, I did get your email...

Keep in touch.

Best,

-AC

Hey Fornax,

Any news about your hrv? Did you get those heat exchangers from recair?

Actually I did order and receive one of those heatexchangers and I did build a new HRV. I have been using it since early october and it is much better than the one I initially build with the aluminium HX-core.
I took a few pictures which I will finaly post here soonish..

In october I collected numbers on temperatures and efficiency but back then the weather was quite warm so the difference in temperature was low giving meaningless numbers. Time for a follow-up indeed :- )

Great, I'm looking forward to have a look! ;)

Hi All,

As I told Kostas above I did build a new HRV using a heatexchangercore I
ordered readymade. It's the exact one some commercial brands are using
in their commercial HRV's and the specs look impressive, it wasn't too
expensive either.

I didn't take a lot of pictures and they aren't the best quality I am afraid
but they do tell the story nicely.

http://ecorenovator.org/forum/member...ox-hx-core.jpg
Bare cabinet with the core in it, playing with dimensions here.


http://ecorenovator.org/forum/member...r-top-left.jpg
Here I added a roster in the top left to put a filter on, it's 30x40cm (12"x16").
One of the fans will be internal, like this. I also added the holes to connect
the tubing.


http://ecorenovator.org/forum/member...ummer-open.jpg
My first HRV didn't have a bypass for when it's hot, I had to remove part of
the plates and block the rest, rather clumsy.
In this one i created a bypass inside the cabinet, this is in the 'open'state.
The two pieces of styrofoam on the fan are used to block it.


http://ecorenovator.org/forum/member...-styrofoam.jpg
Like seen in this picture.


http://ecorenovator.org/forum/member...ed-working.jpg
This is the finished product, working.
It is a bit larger than my first one but it is 16" less tall so hanging close to
the ceiling there's still a lot more room underneith.

Then I took some temperature readings inside the cabinet:
One (luxury) problem I have calculating the efficiency is that the
temperatures are so close to eachother. The middle one is recorded in
the morning when it was freezing a few degrees all night. I get my supply-air
from my crawlspace which acts as a 50m^2 (550SQF) geothermal heating
surface. Also the supply-air is heated a bit while travelling through the tube
in my shed.

With supply-air this warm you could debate wether I even need an HRV... /grin.

After turning off the central heating (20,5C in the evening) at 11PM the next
morning it's still 18,5C in the livingroom and the floor doesn't feel cold (I
added extra insulation underneath it last year and the windows stay closed
now so the bottom half of the livingroom stays warm.) Most of the time we
don't turn up the heat untill after noon.

This plastic HX-core is performing very good, which works fine for me. If your
intake-air is very cold though an HX-core this good creates extra challenges.

Good to see some new stuff here :)
Fornax, I have some doubts about this, though. If you draw the air from the crawl space, you simply recycle it as it comes from your house and not from outside. The fact that it is warm means that you are subtracting air from your home and pushing it back in. I bet you have had no dew inside the case, right?. With no cold air coming from outside there is no reason for condensing the out coming air.... At least that is what those temperatures indicate, inmho.

My crawlspace is outside the livingspace. The floor is made out of concrete with poured on concrete, finished with glued on PVC flooring. Aside of newly created holes it is completely sealed off, it's outside.

I did create 1 hole, where I draw my air from. This fresh air comes from 4 existing ventilation-holes, and thus it comes from outside.

You are welcome to come and have a look, from Italy it's only a day driving, I'll buy you lunch : -)

Seriously though: The air taken in is fresh, it comes from outside. I can prove that with a fryingpan, some oil and some garlic.

Ok then, I'll be there by Sunday :D

How many cfm or m2/h can you push trough that recair exchanger? Was it the 160 model?

Indeed, it is the RS160 model with a heigth of 300mm as seen on www.recair.nl.
Identical heatexchangers (300mm) are used in commercial HRV's that are rated up to 300m3/h. Those HRV's use stronger fans than I do though.
With my fans I estimate some 60 and 120m3/h (lowest and middle setting).

Recair makes excellent exchangers. Indeed, I recently saw one of them installed in a custom made ERV and the fans inside were rated 800 m3/h. :)

I just got my hands on about 8 cubic feet of coroplast for free through Craigslist. I wonder how big the heat exchanger needs to get before diminishing returns just make it ridiculous? IIRC that Danish paper had one about 3x2x.5 feet and it was 80-something% efficient. I'm not sure I'll get around to doing anything with my coroplast soon but I'll try to come back to this thread whenever I start working on it.

I've been thinking more about design.

I originally wanted to make a counter-flow HX, for maximum efficiency, but it seems like sealing up the alternating channels at the ends would be really finicky and prone to leaking. A square cross-flow HX seems much easier, but efficiency isn't as good. So what I'm thinking about doing is simply making many small cross-flow HX's and putting them in series. It would get close to counter-flow efficiency, but is simpler to make. The hexagonal ones seem like a pain to make and still just a compromise between counter-flow and cross-flow. The counter-flow HX is just so elegant and simple, I find myself maybe irrationally biased towards it.

It doesn't get that cold here in Portland, so I'm thinking I could just have a thermistor in the outside air inlet and shut down at the freezing point and wait until it warms back up before turning back on. The house leaks more during deep cold anyway, due to the stack effect. The most useful time for the HRV is during temperate times when there is no stack effect. Also, I could use a microcontroller to make the HRV run at higher CFM for a while when coming out of a below-freezing shutdown period. So during the winter it'd run at higher speed when above freezing, and then not at all when below freezing, while during warm times it would just run constantly at a low/moderate speed.

I'm a little concerned about condensate draining. Creating a sloped pan in the bottom of the enclosure seems like it might be tricky, and how do you keep it from leaking air? A trap will only work during times that create enough condensation to keep the trap full. During spring and fall, the trap might dry out, and then what? Air would be leaking out the condensate tube. Maybe it's a small enough leak (though a small long tube with lots of airflow resistance) to not care.