Viking House,

I sent a private message to Viking House via the EcoRenovator message system, and I also sent an email to seamus at Viking House Ireland, expressing an interest in buying a FiWiHex heat exchanger.

Oddly, neither did the emails bounce, nor did anyone respond to the emails.

I have also sent a query to Viking House US to see if they know anything about this matter.

Viking House, has your health suddenly deteriorated?

-AC_Hacker

"so -11C. That is about 22 below freezing in F."

-11c is 12.2 degrees F.
-20f would be -29c.
0f is -18c

Remember celcius has 0 at freezing while we have it at 32f and our resolution is higher so the numbers get a little confusing in the negatives sometimes.

Hi
I am new to the site, so I am still learning (a lot). Thanks everyone.
I do have a question though. I am interested in the DIY heat recovery ventilator. I don't think the commercial HRVs are very efficient (50-80%) so I haven't purchased one yet.

In an earlier post somebody had the idea of using a hacked AC to cool the outgoing air and heating the incoming air, with a heat exchanger in between them. It sounds like a great idea to me. :thumbup:

My question is- wouldn't it be better to run the stale air through the condensor (?), then straight outside, and run the fresh air from outside straight through the evaporator(?)? My point is I don't see the benefit of using the heat exchanger.
It cools the air going to the condensor (which is trying to gather heat). Although the heat exchanger sends 50- 80% of the incoming heat to the fresh air side, wouldn't it be better to let the pump operate at a higher COP and create more heat? The way I see it the hx saves heat and the pump multiplys heat, using the hx lowers the pumps ability to increase heat. I hope I explained things correctly, I am a long ways from being an expert. Just my $.02. :)

Welcome to ER:)
Actually, if you put a heat exchanger before the heat pump it will have much less work to do (much less heat to move). The smaller the temperature difference between airstreams, the smaller the heat pump can be (= less energy + cheaper).

Putting the HP between airstreams with a large temperature differential will raise the COP (assuming heat is being pumped from warm to cool), but at the expense of using much more energy to move all that heat. Let a HX do most of the work, while a small HP only tops off the system's efficiency.


Also, a HX can partially get rid of the moisture, reducing the risk of icing up the HP. Tempering the intake air with an underground HX helps even more, and allows an even smaller HP.

Hi Piwoslaw,
Great drawing, that describes what I am talking about. I should probably explain the application I am considering. It is winter and I have my crawlspace closed. It would be good to still ventilate it and inexpensively heat the crawl space.
If I understand you correctly, you're saying collect the heat from the stale air before it goes into the HX? I know an ASHP isn't very effective when it is very cold outside, there has to be some heat in the air for it to collect.? I am all for using the HX to save as much heat as possible before it gets vented to outside, but the HX would supply cooled stale air to the HP. I would think that you would want warm stale air going into the heat pump so it can push hot fresh air out.
Some HRVs use an auxillary heating element in the duct that vents fresh air into the home, but it would be better to use an ASHP with a high COP. From my understanding HPs have a higher COP, (produce more heat) when there is lots of heat to be collected. That is why I am thinking that a HE is counterproductive. With a HP the temp on one side depends on the temp of the other side.?
I agree that a smaller heat pump would be better, but between two heat pumps I would choose the one with a higher COP, and I think by supplying warm air to the HP it would achieve a higher COP.
I like your idea of the ground heat exchanger. I did some informal research on an "Earth tube". Most people who use them report mixed results. Some say the moist warm air cools on it's wall and causes condensation in the pipe, which collects dust and eventually mold. I would think you could clean it like a chinmey, so a little maintenance isn't really a problem. One guy I spoke with said it didn't really change the temperature much. He recommended that instead of one large pipe it would have been better if he had used many smaller pipes connected to a manifold. Of course the required lengths and depths of the tubes is a whole other topic.
I will say though that I have considered connecting a HRV to a solar air collector. But like the HP, I think the HE would cool the air coming from the solar collector, and be counterproductive to what I am trying to accomplish. Would it be better to not try to combine all these things?

No, collect the heat after it has gone through the HX, ie the heat pump is between the two outgoing streams - one going out of the house (cooled stale air) and one going out of the HX into the house (warmed fresh air).

Look at it this way: Assume that the air in the house is at 20°C/68°F, while outdoor temp is 0°C/32°F. If the HX is 80% efficient, then the airstreams leaving it should have temps: 16°C/61°F (housebound) and 4°C/39°F (outbound). Now put a HP on those two to extract heat from the cold stream and cool it to 0°C/32°F, warming the housebound stream to 20°C/68°F. The HP will be pumping "against the temp gradient" to carry over those 4°C/7°F, so its COP won't be too high (though that can be slightly improved by increasing the size of the evaporator and condenser coils).

Now, imagine a HP which has to totally switch the temperatures of the two ingoing streams: It has to cool one stream from 20°C/68°C to 0°C/32°F and warm the other by the same amount. This may seem like good potential for a higher COP, but that is only an illusion. It would be true if you were taking up to 10°C from the warm stream and feeding it to the cold, but you'll still be using electrical energy to do that - it won't flow for free unless you use a HX. Once the two streams' temperatures evened out you'd start pumping "against the temp gradient" again, only with each degree that gradient will get larger. At some point (assuming you are increasing the size of the heat pump) you'll have the warm, stale stream cooled to 4°C/39°F and the fresh stream warmed to 16°C/61°F. Now what's left is the same situation as in the HX case: a 4°C/7°F temperature difference against the gradient. So, summing it all up, you'll be doing all the work as in the first case, plus lots of extra work just to cool the warm stream from 20°C/68°F to 4°C/39°F and to warm the cool stream by the same amount. At the beginning the COP may have been high for a short time, but in all you used much more energy just to do what a heat exchanger does for free.

The energy needed to counter extra pumping losses through the HX is negligible.

Ko_deZ,

As I recall, you said that your heat exchanger is made of aluminum. and that it is about 1 meter long and about 10 cm by 10 cm, and that it is counter-flow, is that correct?

I wanted to build an experimental version similar in construction to your, only from plastic (I know it will not be as good).

I easily can see how I would build the counter-flow, but I don't see how I would get the air flows into the counter-flow structure.

Could you post a photo of your HX core? I am drawing a blank here...

Thanks,

-AC_Hacker

This is the one I have, with the front door open:
http://ener.no/filestore/E101600K.pdf

The pipes going out of it is 200mm, so I guess the heat sinks are ca 20cmx20cmx100cm.

The principle is like the added drawing. By alternating the airflow with the airflow switch (SW in the drawing), the heat-sinks are heated and cooled. The switch is done just before the heatsink is completely cooled/heated. As you can imagine, there will be an area where most of the temperature change happens that is not very long on the heat sinks (guessing 10-20cm) that will move towards one side or the other depending on airflow direction. In practice you get a counter flow HX, only that you do this using two heat sinks and alternating the direction instead.

I like the principle. It avoids having the constantly moving wheel and airleaks that a rotating HRV has, and also avoids the humidity loss/gain and icing problems that a standard counter-flow unit has. This thing will do humidity recovery which significantly reduces the icing, and in a humid summer day reduces the energy needed for cooling (less condensation). There still might be a little icing in this unit, but until now, I have not seen any. We have not been below -10C (10F?), so I cannot say for sure yet. I can say for sure though, that a normal counter flow unit would have had icing problems already. That unit Viking was talking about would certainly be icing up in our current conditions. Wonder why he never answered my questions regarding that :p

Ko_deZ,

Thanks for the picture.


From that photo and this diagram:


I estimated that the cores are 100cm x 20 cm x 50 cm. The 50 cm dimension is if the HRV does not have a false back, I can't tell from the photograph, but the drawing indicates that the cabinet is 52 cm deep, so I assume that the cores go full depth.

I guess the "switch" is a rotating wheel with baffles that allow air to alternately flow through one exchanger and then another.

Here is another similar HRV that uses a similar air flow principle:


Here's inside view:


They even have a video of the thing in action... it is not youtube, so it takes a while to load.

I think the one you have is obviously designed for better efficiency.

-AC_Hacker

Hi.

There is a false back. That is how the airflow gets where it is supposed to. The doors have rubber gaskets on them ensuring an airtight seal. They might be as much as 30cm deep though. Cannot say for sure.

Interesting video. Yes, same principle, but way too small heat sinks. It is the length that is the secret I believe. My unit switches about every 50 second. Also, having the input/output vents beside each other will give you a bit of air just looping and coming back in.

-Ko_deZ-

HRV + Heat Pipes + Hillbilly + interesting monitor... (part - 1)
 

Met a very interesting "mad scientist" the other day...

He is reluctant to post his work, gave me permission to do so.


(* 4-part post begins here *)

I had my house insulation upgraded and some leaks sealed.
I'd like to do more sealing, but will need some external ventilation.

I read that, for a well-insulated house, 40% of the heat cost goes
out the window (so to speak) as fresh air infiltration.

I looked into Heat Recovery Ventilators. Cheapest I could find was
$400 on ebay. And that doesn't include shipping or all the mounting and piping
and electrical work. Quotes for installed systems are over $1000.

That ain't gonna happen, so I started looking at DIY solutions.
Found web page that described a cross-flow heat exchanger for
dryer heat recovery. It was made out of corrugated plastic sign material.

I was concerned that the thermal conductivity of the plastic would be
insufficient, but I built one anyway. Tests with a heat gun and a fan
concluded that it might be OK. I was sufficiently encouraged to embark
upon a quest for a cheap plastic HRV.

The day after an election, 24" x 18" corrugated plastic signs are free.
Finally, something useful from politicians!!
Even in off season, they're not hard to find. First sign shop I tried
was kind enough to give me a stack of old signs.

The problem was coming up with a design that could be built
with resources found in the average kitchen drawer.

Here's what I came up with:.
Has basically one part repeated multiple times.
Should be able to construct it with a linoleum knife and some
shipping tape to seal off the channels.

Cut the sign in half to make 24" x 9" plates.
Cut notches in the end and triangles in the interior.
Tape off some of the channels.
Flip and interleave them for a stack height of 3".
A 4" round duct pipe coerced into a square should fit
nicely over a 3"x 3" stack of plastic.
Depending on mounting, wrap it with fiberglass insulation
or sandwich it between two chunks of rigid insulation board.



There are issues with ducting and water drainage and mold growth that are not resolved.

To maintain the true hillbilly spirit, my first attempt will be to forgo the ducting entirely.
Cut a rectangle of 1" insulation board that fits in the window channel.
Glue this Hillbilly HRV to the outside.
Cut holes for the top air in/out and duct the air into the house with a chunk
of sign board and some duct tape.
Place an old computer fan over one of the holes to force air in or out.
Depend on the house being tight enough to make the air go the other way.
Can always add a second fan if required...or better yet, more leak sealing.
IF the wind is blowing, the hillbilly HRV can stop working, but in that case,
you've got plenty of ventilation thru leaks anyway.
Use a plastic deflector so the water that drips out will miss the side of the house.
Stick a second layer of insulation on the outside to complete the plastic sandwich
within the insulation sandwich.
Depend on baffling to reduce the mixing of the in/out air on both sides.
Tape some filter material over the outside openings to keep critters out.

This is NOT an optimal design. It's a LOW price/performance attempt to
get a significant percentage of a real HRV for almost ZERO cost.
It's also important that it can be easily constructed by the average person
(ME) with stuff found in an average kitchen drawer..
Put it on the backside of the house obscured by bushes and your neighbors
will never know your house looks like it belongs in a trailer park.
Or paint a picture of your cat on it. Your neighbors will think your cat
likes to sit in the window.
And you can remove it in seconds when you invite your boss to that dinner
party.

I can run the fan off a UL approved laptop power supply so the gumment
inspectors don't get their panties in a wad. It's not permanently attached.

It rarely stays below freezing for long here, so defrosting is not an issue.

I can improve the thermal efficiency by cutting big "non-overlapping holes in the
board, but that can seriously compromise the dimensional stability. It really needs
to hold its shape when you build the sandwich. And it needs to come apart for
cleaning without breaking the plastic.

My biggest concern is how to keep nasty mold, mildew, etc.
from growing in it.

In the spirit of "measure twice, cut once", I'd like input before I go wasting
all my free sign material on a flawed design.

Ideas?
Thanks, mike


7/22/10
Well, didn't get any input, so I built one.
All the plates are identical


Flip every other one so all the triangular holes get covered by plates on either side to form
the serpentine air path.

It's a folded axial-flow heat exchanger
with three parallel air paths...per sheet. Every other sheet
carries air in through the plastic channels that make up the corrugations.
Alternate sheets carry air out.
Heat is exchanged thru the flat sides of the plastic sheets.


Haven't put on the tape to Block the relevant channels...yet.


First Prototype:


-AC_Hacker

HRV + Heat Pipe + Hillbilly + interesting monitor... (part - 2)
 

(* 2 of 4-part post continues here *)



BIG PROBLEM
Too Restrictive. Can't get enough air flow through it.
Does seem to be transferring heat though.
Needs to have bigger channels.

Heat Pipe Version

While I look for cheap aluminum plates for the flat plate exchanger,
I looked at a heat pipe.

1/4" copper pipe. The gizmo in the center is the piercing clamp that is designed
to add freon to an exixting air conditioner. ..with a R12 to R134 adapter.
Clamped the ends shut and soldered.
Added R134.
Need to learn to tell how much liquid is in there.
Seems to transfer heat quite well. But coupling hetat into the pipe needs work.

Really can't make use of the curves...radius is too large.


Vertical straight pipes look like a better solution
Not my idea. Found a similar design on a website that I can't remember.


Valves from old bicycle tube


-AC_Hacker

HRV + Heat Pipe + Hillbilly + interesting monitor... (part - 3)
 

(* 3 of 4-part post continues here *)

Hard part was filling it. Rube Goldberg setup of all the pieces
it took to get from one thread to the Schrader valves.


I used ice on the copper to condense the gas while filling the tube. Takes several minutes.
Put in some and vent it to clear the trapped air. Then fill it.

When it's done, you can tell how full it is with a heat source and stethoscope.
Listen to the tube and move the point heat source up and down on the pipe.
Starting at the top, move the source slowly down the pipe. When you hit the liquid
level, you can hear it boil. If it's too low, add more...too high, vent some.
For a heat source, I use a tiny catalytic hot air attachment for a butane soldering iron.

CAUTION, this stuff is cold. Wear gloves and wrap in insulating material. If it vents
on your hands while you're trying to hook it up, it will give you FROSTBITE.
EYE PROTECTION IS ESSENTIAL...DON'T GO WITHOUT IT.
LIFE IS HARD ENOUGH WHEN YOU CAN SEE.
USE ADEQUATE VENTILATION.
DO NOT ATTEMPT TO DO THIS.
FOR EDUCATIONAL PURPOSES ONLY.
UNSAFE PROCEDURE.
DON'T DO IT!!!!

Next step, transferring heat from air to the pipes.

Made some fins out of .040" aluminum


The resistor is an attempt to have controlled power input. At 25W, the resistor temp
is WAY above the pipe temp. Lots of losses getting from heat source to the refrigerant.
The line about 1/4 the way between the fins is the liquid refrigerant level.



-AC_Hacker

HRV + Heat Pipe + Hillbilly + interesting monitor... (part - 4)
 

(* 4 of 4-part post continues here *)

The heat pipe is doing its job. Getting heat in and out is problematic.

I finally did the math I should have done earlier.
Using round number approximations:
In winter, assume it's 35F outside and 65F inside. deltaT of 30 degrees.
100cfm of air exchange with outside sends 1.08X100X30 = 3240 BTU/Hr. = 950 Watts..
Assuming we can save 500W of that, the effective thermal resistance of the system
has to be 30/500 = 0.06 degreesF per watt!!!
I need MUCH bigger heat pipes ;-)


Test Jig
Best temp differential I've seen this summer is about 15 degrees F.
Inlet air temp is about half way between the inside and outside temp.
But the margin for measruement error is a significant portion of that.
Need much hotter or colder day to get the temp differential up.


Fan overlay


November 2011
BETTER HEAT PIPES

I bolted a pair of computer CPU heat sinks back to back and mounted them in the window.
I haven't done much evaluation, but the incoming air temperature seems to be midway
between the internal and external temperature. That seems high. Need to do something to separate
the airflows to keep them from mixing. Also need to close up the air leaks in the heat exchanger.

I also noticed that, in calm weather, the air close to the house is warmer than the "outside temperature".


The results here led me to experimenting with water-based heat pipes.
Some quick tests suggest that, while they may work fine for computer
chip temperatures, at HRV temperatures, the vapor pressure of
water is so low that it can't overcome the weight of the water
column. Evaporation is confined to the surface of the water
column and little heat is transferred. The computer heat sinks get
around this using a wicking structure and no standing water column at all.
I have no confidence that I can duplicate that in my garage.
Freon seems to be the best choice for DIY experiments.



ROCKS



Somebody suggested I use a reciprocating HRV using steel balls as the storage medium.
I like rocks. Sounds strange until you do the math.

Basically, you blow air out of the structure through the rocks. This heats the rocks
in winter or cools them in summer. The average temperature of the rocks is
half way between inside and outside temperature. You don't need much temperature change.
After some time, you reverse the fan and pull outside air back through the rocks.
This recovers heat from the rocks.

In winter, moisture from inside condenses on the rocks and drips out the bottom, so it
doesn't come back on the next half-cycle. This performs one of the primary functions
of the HRV, reduction in internal humidity.

You're still blowing air in and out thru cracks in the structure, so you get only half the potential
heat savings. Two units out of phase equalize the pressure and should double the efficiency.
If the units are in different rooms, you get some internal circulation.
It also solves the piping problems with routing air all over.

Major design hurdle is the fact that most fans are not reversible. This needs some
research. The rest looks simple.

Stack up six cinder blocks on top of a grate.
Some baffling to reduce intermixing of the flow.
Fill up the holes with river rock.
Wrap it with insulation.
Pipe air to each hole, run them out of phase.


MONITOR

In addition to monitoring temperatures and airflow, I also track the amount of time the furnace runs.
This gives a running commentary on how well, or badly, an experiment is working.


The numbers are :
sample number, % run time this cycle, average % runtime since start, minutes furnace ran this cycle, length of the cycle in minutes, outside temp.
The outside temperature reads zero because the sensor is not plugged in.
The graph represents one day with noon in the center. Each line segment is a furnace cycle. Length of the segment
is relative to the length of the run-time, but had to lengthen them to make 'em visible. Vertical position is the percentage
on time for the cycle. That represents the BTU/hour for that cycle.
Each percentage point represents an average heating power of 170 watts. I can watch the gas furnace output go up
when I turn off my computer.
Green blip at the baseline is the current time. Everything to the right of the blip is yesterday's data.


-AC_Hacker

HRV + Heat Pipe + Hillbilly + interesting monitor... (complete)
 

4-part posting of:

HRV + Heat Pipe + Hillbilly + interesting monitor...

...is now complete, all in-line images are working correctly.

-AC_Hacker

HRV Energy-Savings Program...
 

Here's a link to a German company that makes HRVs... wheel-type, cross-flow and counter-flow.

Klingenburg GmbH - Energy Recovery

They have a program that will calculate amortization due to energy savings. It just so happens that it will approve (or not) HRV cores dimensions that will work for a given airflow, thus it can be indirectly used as a design program...

http://www.klingenburg-usa.com/pdf/Wirt.zip

The program just runs, apparently there is no install, it just runs.

-AC_Hacker

Strange that this thread has headed down a similar path that I have been working on. I agree with the issues on the heat pipe as a starting solution. I think there is some possible solution mixing fine wire mesh interconnecting several heat pipes as has been fabricated in the pictures. The fine wire will transfer more heat energy between the sources than using the fins shown in the pictures. The fine wire will create more turbulence thus mixing the air as it passes across the wires. Another problem with the heat pipe solution is that heat pipes want to function better when the hotter temperature is on the high side and the colder on the bottom. This would mean that these heat pipes would need to reverse themselves when the "delta T" in and out reverses. In other words at least fall and spring they would need to flip. In the Summer the cooler inside air needs to flow across the bottom of the heat exchanger and in the winter the cooler outside air needs to flow across the bottom of the heat exchanger. The more heat pipes the faster the transfer of heat energy. Likewise the more interlacing of fine wire to make the system work and more laborious the task.

The heat pipe that Mike showed me had liquid Freon that was more dense and was at the bottom of the pipe, and Freon vapor was filling the top of the pipe.

Heating the bottom of the pipe caused the liquid Freon at the bottom to boil and the vapors rose to the top of the pipe where they condensed and released their heat and returned as liquid, to the bottom of the pipe.

-AC_Hacker

Yes you are correct I had my logic reversed. The heat pipe would still need to flip over or the outside incoming air would need to switch locations in order to make the process function correctly.
I have also looked into a thermoelectric peltier unit to be the heat exchanger with two heat pipe fine wire systems one on top of the thermo unit and one on the bottom of the unit. You would switch polarity of the unit when the inside/outside delta t reversed. These units were $6 before christmas. They have doubled in price since christmas.
Adding this thermo component reduces efficiency drastically.

Hi,
I like the "Mad Scientist's" inventions. How big is the coroplast that he is using for his heat exchanger? It seems logical that more surface area in a heat exchanger will increase efficiency; however, I think all those turns are causing the problems.

The vertical pipe heat exchanger is great. It seems very similar in principal to an evacuated tube solar collector.

I found this heat exchanger, which is kind of different, so I thought I would post it for discussion.

It is basically a heat pump which recovers heat from the exhausted stale air, and supplies warm air to the fresh air supply side. It doesn't use a "heat exchanger". I had this idea a few weeks ago, and now I found that somebody actually makes one. It was also pointed out that this kind of HRV would be more efficient if it used a heat exchanger. I couldn't find a lot of information about this HRV and everybody is out for the holidays.

I'm not sure if it posted with the picture, if not, then here is an excerpt from their advertisement.

ThermalAir is a programmable air exchanger which saves energy and dehumidifies the air. We would like to say that it keeps the heat indoors in cold climate and retains the cool inside in summer but this would be an understatement because ThermalAir is more than 100% efficient. ThermalAir will extract 9,958 btu's of heat from the outdoors in winter and blow the warm fresh air indoors. Conversely, in the summer it will blow 6,284 btu of cool fresh air indoors. ThermalAir is supper efficient at 390% in heating mode and 710% cooling mode, this means for example, for every watt required in cooling mode to run, ThermalAir returns 7.1 watt of cooling output. Now that's green and bonus: it provides 15,600 cubic feet of fresh oxygenated air per hour!

Attachment 1984

I think the coroplast for his HX attempt was about 3' x 1'. The idea was very clever, but the resistance to flow was too high.

He is having trouble getting a significant amount of heat into and out of his heat pipe HX. The fins he put on were not doing the job.

One name that is given to units like this is "active HRV". I have seen units similar to this being marketed in Europe (where the cost of energy is 2X what ours is, and the effort being put into energy efficient designs is also 2X). These units are sometimes referred to as 'combi units'.


Here's a link to specifications on one unit that is an HRV, Water heater, solar assisted, and apparently a home heater, too (assuming uber insulation).

I really like the Thermal Air concept.

-AC_Hacker

Hi,
I just got off the phone with a representative of Thermal Air. The company is in Florida. The HRVs are manufactured in Canada. They are kind of spendy at $2,800. :(

One thing he pointed out which I kind of liked was that since it has two fans it is possible to adjust the speed of each independantly. Since most homes aren't 100% air tight and have a little leakage, some people turn down the exhaust speed and turn up the incoming fresh air speed a little.

This provides a little positive pressure to overcome any leaks in the house envelope. I wouldn't want to set these too far out of balance, because it would only waste energy; however, IMHO it is better to have a little positive pressure instead of a negative pressure, which would only suck in unconditioned air.

Another reason I like these is that a standard HRV is about 80% efficient; where as, the thermal air has a COP of 3.9 and an EER of 7.1. I know it would still use more energy than a standard HRV, but a standard HRV will blow cool fresh air into the house during winter. The heat pump HRV will blow warm fresh air in the winter, and cool fresh air in the summer. The heat it blows into the house would "lighten the load" for your primary heating system. The simplicity of this design makes it a good candidate for a hack. :thumbup:

AC: that Combi 185 is great. Although it is a much more complcated system it is much better. Using a Heat exchanger with the heat pump allows the heat pump to work less: that in itself makes it a better option than the Thermal Air. But, it also produces ~80 gl of hot water per day by working as an ASHP. I am sure they have it balanced out to where it doesn't take more heat out of the house than what it is supplying to the house, at least in the winter, in the summer this would work great.

I really wish our country would get with the program, great products are being made, but not in our country and we can't even import them. The Combi 185 uses 220V since it is made for the German market. It would be possible to use a transformer to step up our 110v to 220v; however, the transformer would provide 220v @60hz (in the states) and the machine is designed for 220v @50hz.

It is a very interesting time to be following these new inventions. And I am sure it is only a matter of time before they show up on our shores.:)

With a pressurized house, you are pushing warm/moist air out your leaky path. There is a possibility of moisture build up and mold growth. Balancing them as much as possible would probably be better.

"This provides a little positive pressure to overcome any leaks in the house envelope. I wouldn't want to set these too far out of balance, because it would only waste energy; however, IMHO it is better to have a little positive pressure instead of a negative pressure, which would only suck in unconditioned air."

If the pressure isn't balanced, you want negative pressure in the winter and positive pressure in the summer. This is because the dew point inside the house is more likely to condense inside leaky areas going outside during the winter. In the summer the dew point on a hot day is usually above the temperature that is inside so a positive pressure is a good idea in this case.

These are all really good comments.

A small dehumidifier has all of the components to make one of these things...

Except that you'd want more efficient fans.

This would be a really interesting hack, and pretty easy, too.

There's just one thing about these units, they supply a VERY LARGE amount of air. I looked at the Combi, thinking that it would fit so nicely into a cozy, compact, space-efficient European house, then I calculated how much space it could actually ventilate, and saw that it could supply the ventilation needs for a 3500 sq. ft. house... and that's with a (quite small) 350 watt compressor, too. To be clear, that was on high speed, but that's a lot of air...

I haven't written the idea of it off, not yet... I did see a tiny cube refrigerator today at Goodwill that had a 125 watt compressor, for $25. Now that's more my size... and I have a couple of very small HXs left over from my first GSHP project...

Oh the temptation!

-AC_Hacker

A few days ago, I went over to Mike's (AKA: Mad scientist Guy) to do some testing on the coroplast squares I bought a while back.


Here's a photo of the test setup:


You can see the heater blowing into the air input of the centrifugal fan at "A".

I put some heavy stuff on top of the coroplast to make sure that it was in good contact.

We ran quite a few tests, here is some of the non-conclusive data we recorded:

Ambient temperature of testing lab (AKA: Mike's garage) = 53F

Heated airflow was from A to A'

Recovered airflow was from B to B'

No heat:

• A = 56.2F
• A' = 56.0F
• B = 52.3F
• B' = 54.5F

After several minutes of heat (Heater drew 1092 watts):

• A = 101.4F
• A' = 83.8F
• B = 54.7F
• B' = 77.5F

Increased Fan (B, B') voltage to 12V

• A = 102.2F
• A' = 80F
• B = 55.8F
• B' = 75.9F

Reduced fan (B, B') voltage to 7.68v

• A = 144F
• A' = 86F
• B = 55.9F
• B' = 78.4F

THOUGHTS:

• It does work, but the results are not stunning.
• It works better than no HRV.
• The low numbers were most likely affected adversely because the core was in ambient (low temperature) environment.
• It really make me want to see how a counter-flow coroplast HX would work.
• We need to capture data that would give us an efficiency measurement.

-AC_Hacker

Mike Does Weld Test on Coroplast...
 

Mike came across this patent on making coroplast HRV cores. and shortly after, Mike sent me his initial results of trying to weld coroplast (polyethylene)...


-AC_Hacker

Nice numbers, AC and Mike:)

Over at the Polish builders forum someone posted this:

Apparently, it is a PP coroplast HX, produced by Canadian Greentek, which claims its efficiency matches that of other (metal) crossflow heat exchangers.
From the images above it appears that the HX is not made of squares of coroplast rotated 90°, but instead the squares have spacers between them. This has two advantages: lower pumping losses (on one side) and single walls (instead of double) between airflow streams. Could you guys try a test with spacers?

Fantastic Coloroplastic
 

Mike has been at it again:

The 'stale air' temp drop improved to 30 deg F., but the 'incoming air' DeltaT got worse. Why would that be? Previous to that the DeltaT was approx. 20 degF on both. Go figure.

There were so many thing that were changed between experiments that it would be pretty risky to compare results from one day of testing a particular HX to another day of testing a completely different HX.

Perhaps we will repeat the experiments with an effort given to minimizing variables.

I'm planning to make another HX for testing, and I wouldn't be surprised if Mike intends to test other configuration(s) too.

-AC_Hacker

How do you measure differential pressure?
 

I want to measure differential air pressure near zero.
I have a pressure gauge, but it has a resolution of only
0.01" of water.
I tried building a gauge using a resistor heat source with a thermocouple
on either side connected in a bridge. Stuffed that into the side of
a plastic tube. Air flow causes differential heating in the thermocouples.
It sorta works. I get about 200mV of bridge imbalance for a differential
pressure of 0.04" water. But the time constant is half a minute.
It's not temperature compensated, it drifts. I could use it to measure
zero, pressure balance...but I'd like to make it better if it's easy.

What do you guys use to measure low pressures?

Why do I feel cold?
 

I stuck an experimental HRV through a window in an unused bedroom.
The bedroom opens into the hallway just beneath the gas furnace
return vent and the thermostat.

It's a small coroplast unit about 4" square by 2 feet long.
I'm guessing it's 15-20CFM. Air velocity varies considerably
over the port area. I'm gonna have to build some kind of
"air straightener" tube before I an get an accurate flow
measurement.

AC Hacker posted some pix of it last week.

Since I turned it on, the place smells less stuffy. I like the effect.
Problem is that I feel COLD!!!
Temperature is still 64F. Humidity still about 50%.
I even turned the thermostat up to 65F. Better, but I still feel cold.

I figured it was all in my head, 'till my neighbor came over and commented
that the place felt colder than usual.

Inside temperature and humidity have not changed.
We're having record warm weather outside.
What mechanism can make it "feel" colder when the numbers are the same???

It's weird that you mention that because yesterday I had my windows open and the temperature was 3 degrees higher and the humidity was 1% lower but it felt like it had gotten colder. It aired out the afternoon bacon frying smoke though. Is it a draft thing? I wonder if the air continues to move at a faster rate than normal after the windows are closed because now its the next day and things feel normal and not cold again even though its below the temperature it was yesterday in here.

Welcome ham789 and have a Great 2012!
73,

I know a few people who use BP meds or other meds that can reduce blood flow who say it makes them feel more susceptible to cold. If you are warm with a workout, it sounds like a blood flow thing. ...then again same thing can happen if you are cold too since moving around can warm you up pretty quickly.

Were you comparing out door air to indoor air?

I have noticed that in the shade it feels cooler because of the larger amount of moving air that moves the heat from you. Indoors the heat would slowly move away from you into the space (small) that you are in. And there is no solar effect.

This thread is about building a Heat Recovery Ventilator...

The Billard Room would be the perfect place to discuss subjective effects of blood pressure meds, etc.

-AC_Hacker

Yes, indoor air after the windows were closed, so its fresh air that recently came from outside.

I like the dehumidifier idea (posted near the beginning of this thread). What about placing the evaporator coil in the cold/stale air going out, and the condenser in the cold/fresh air coming in? Basically putting a small HP on the outside air portion of the HRV system. Dehumidifiers don't use much electricity. It seems to me like that would greatly improve energy recovery. The HP would not only be using the heat energy from the incoming air from outside, but also the heat that the HRV doesn't recover. To me, it seems like this system would produce much more heat than an air-air HP located outside. Ductwork could be made to reverse the system during the warmer months.

EDIT: oops, got my condensers and evaporators confused :o