I think you should be more than a little concerned, HRV condensation is a major issue here in PDX.

A previous PDX poster to the thread made a simple cross flow chloroplast rig that was about 2 feet long and about 6" x 6", using a computer fan. He had it tilted a bit, so that it was self-draining.


It dripped and drained a bit, but it dripped and drained constantly.

If you had a strategically rigged drain pan and a small plastic tube, it would self-drain and there would be minimum air leakage.

BTW, I like your series cross-flow idea.



-AC_Hacker

Any time you are doing heat transfer, there will be condensation. During the summer, the fresh warm air from outside will shed some water on its way in. During winter, the stale warm air will shed some water on its way out. The only exception is in the desert or dust bowl during some of the summer. Even there, if it's really hot out and you have air conditioning, some water will condense.

Make sure to include drip edges and a drain in your enclosure. Leave no space for water to stagnate, and put a p-trap in the drain. The small pressure difference (millimeters of H2O) will not overcome a half inch p-trap.

Also, make sure to put filters on the intake sides of both flow paths. These cores like to clog up with dust. Bugs love to make homes in the cores also (especially spiders), so put screens on the outdoor ports to keep them from invading.

The lifebreath unit:
http://www.hrvinfoline.com/images/dblcore.jpg

Functional sketch of the lifebreath:
http://img.photobucket.com/albums/v4...heets/hrv2.jpg
Notice the defrost damper on the fresh air inlet. I believe it will rotate to close off the fresh air port completely when defrosting.

The frigate unit:
http://vents-us.com/images/image/Fri...isanie-500.gif
Notice the fans are in the center chamber and no defrost damper. The unit defrosts by running exhaust air only.

You can route ducts for these things many ways. Check out this thread:
http://www.doityourself.com/forum/du...uestion.html#b

Run your intake air through a few meters of buried tube(s). That way it will be precooled in the summer (and slightly dehumidified) and prewarmed in the winter. Not only does this increase the system's efficiency, but also if sized correctly, the intake air will never be below freezing, so no defrost will be required.

Piwoslaw,

I agree with the concept for sure, but I think your idea of "a few meters" may be a bit naive. You may be underestimating by a factor of 6.

Most earth-tube designs I have seen call for lengths of around 30 meters.

But your principle is sound.

-AC

Here are some photos of a DIY Heat Recovery System I built last summer with the help of info in this thread.

Like previous posts the core is made from Corex sheets and Corex spacer strips stuck together with double sided tape.
The case is made form laminated MDF, the fans are 48VDC ones I found on Ebay which are controlled by an Arduino, the gold box on top of the unit is the 48V PSU.

There are temp sensors in the four inlets/outlets which are read by the arduino and which can be monitored by myself via my PC.

I built the unit to bring down the relative humidity in my house during the winter, as I found myself opening all the windows during the cold weather for ventilation.

last winter was mild in the UK and the lowest input air temp I saw was about 1*C, with an extract temp of 20*C I was seeing about 16/17*C Supply air to the house, if I remember correctly. As long as the external temp was below 8*C the internal Relative Humidity was between 45-55% where it had been closer to 70% without the heat recovery.

The unit could still do with a bit of work with regards to insulating the ducts as it lives in my loft. You can see the aluminum drip tray which deals with most of the condensation, although I do get some condensation on the internal surfaces which may shorten the life of the MDF case. A better case design would allow all the condensation to run down to one point, or build it out of something water resistant.

When I first ran the unit I didnt connect the condensate drain which seemed fine until the outside temp dropped to below 10*C it then started producing about half pint of water in 24hours

When winter returns ill post some screen shots of the temp sensor readings

http://ecorenovator.org/forum/attach...0-09-47-50-jpg

http://ecorenovator.org/forum/attach...0-09-48-27-jpg

http://ecorenovator.org/forum/attach...0-09-48-33-jpg

http://ecorenovator.org/forum/attach...0-09-48-49-jpg

This has turned into a long thread, but totally worthwhile.

Thanks to all contributors for the last 4 years or so of fantastic information and inspiration. :)

Apologies from me for making a long post, but on topics like this enough detail needs to be given to solicit quality responses without lots of follow up posts!

----

I'm researching the design/construction of a HRV for an old wooden boat we're completely restoring/renovating. I'd like to run some design aspects/choices past the audience and ask for feedback/advice please before they get locked in.

To empathise, as it's a boat, power (aka never enough of it, aka electricity) and keeping costs under tight control are the two major factors.

Also due to the nature, I need to plan all of the major works (electrical, plumbing, HVAC etc in whilst I'm working on the Hull/Superstructure). So important to get it 'mostly' right from the start!

So, to our own HRV design...

Proposed HRV design

Three Counter Cross Flow cores in series. Each ~243mm x 243mm x 346mm (~ 9.5" x 9.5" x 13.5"), constructed from 2mm Correx (extruded polypropylene, aka the estate agents sign material as discussed at length here). The size is partially determined by the size of the fans.

I appreciate that 3 cores is perhaps overkill and suffers from diminishing returns. Still, the Correx is very cheap and a small proportion of the costs of building a HRV. Lots of surface area and the 2mm has thin walls.

If air resistance of the 3rd core proves to be too high a cost to pay (compared to the extra ~10% efficiency) then I can leave it out but I'll start off with it in.

Airflow

4x 48V DC 13W 0.27A high efficency axial fans, each yields 226CFM. 172mm (6.75") in Dia. 47 db(A) at full tilt means they are fairly quiet and when they are enclosed with the HRV cores and tucked away in the 'mechanical' room means we'll never know they are running (cross fingers).

Two of these on the input and two on the output. A total of 452CFM for each of the flow and return BUT I only need 400CFM to acheive 6 Air Changes per Hour. I'll PWM these down to the 85% of flow for 6ACH, 42.5% for 3ACH (or drop down to 1 fan per leg) etc (whatever saves the most power).

Depending on time of day and temp/humidity conditions measured throughout will influence the tradeoff between ACH and maintaining the target temp/humidity selected on the 'thermostat'.

Filtration

A cheap, fairly coarse, air con/HRV disposable filter on the Fresh Air In, and I'm hoping to source a HEPA H14 filter for the Fresh Air Out.

A HEPA H14 grade filters down to 0.3µm so is good enough to stop Legionella spores. I don't know if the resistance of this filter will be a show stopper or not yet. I could add more fans (I can get them dirt cheap, and they are energy efficient).

Heating/Cooling

I've also pencilled in two water/air heat exchangers (Honda motorcycle 'radiators') that I'll be passing water through.

Hot through one, cold through the other (not at the same time, motorised ball valves under microprocessor control which, if either, is on). I'm expecting the hot radiator to add 2-6°C depending on air flow. The cold radiator won't be nearly as effective, possibly 1-2°C due to a much lower deltaT, but every single degree of cooling helps.

(Two radiators make the plumbing design simple)

Condensate drainage

I've allowed space for the condensate to collect and the microcontroller will monitor the water level and activate a small DC pump to remove that from time to time.

Humidifier/De-humidifier

Pulling apart a cheap ultrasonic humidifier could be a nice touch. Removing the integral large water reservoir and feeding the water from an external source make them quite compact.

A cheap one can inject 480 ml/hr. In rough numbers that is enough to drop the temp by 2.5°C (I think). However 3 ACH's drop this to @1°C of course, 6ACH's = ~0.5°C. Perhaps something that can inject 1000 ml/hr may be a better choice.

Of course maintaining RH is important but remember this is a boat so higher than average RH on the input compared to a house.

De-humidifier. I'm not so keen on integrating this internally. I can always add this 'feature' at some point if humidity is ever a problem by using one of the portable units as my gut tells me it may only be an issue in rare circumstances (given the number of ACH's the HRV can do, after all a HRV acts somewhat like a dehumidifier as a side effect).

Some background info/factors:

I've roughly calculated that due to the volume size, the amount of insulation etc. that a 5KW water heater (for heating & domestic hot water supply) will ensure a ~20°C internal temp IF we fit a HRV that manages 50% or better under external conditions down to ~-5°C.

Volume: It's not a massive boat, in round numbers 4,000 Cu. Ft.
Insulation: Good, not far off a typical house (double glazing etc).
Location: UK (so Winters can be cold - say -10°C. Summers can be hot - 32°C yesterday for example)
Power: 48VDC (from batteries, generator & solar - shoreline 230VAC at times too)
Air Changes per Hour: between 1 & 6, depending on time of day and environmental circumstances (IE it will be dynamic)
Control: Microprocessor controlled, Temp/Humidity constantly measured everywhere of course.
Heating: As mentioned, a 5KW diesel water heater provides hot water. This would be used for domestic hot water and underfloor radiant heating.
Cooling: As it's a boat, we're sitting on an unlimited supply of 'cold' water. 5-12°C is typical. This would be utilised via a water/water heat exchanger to the 'dirty' water isn't used directly inside the boat of course. This cooling source will be used for other things too.

I prefer this kind of fan, it has the ECM motor integrated into the hub, and is quieter and more efficient.

-AC

What make/model (URL if available please) are those? How many ACH's etc does your setup do? Any issues with maintaining flow/pressure?

I've already bought the fans but it would still be good to compare/contrast. I can't do inline images or URL's yet (due to low post count) but images.google for 109E1748H502 will quickly show what I have (quite common in top of rack cooling solutions so plentiful from IT refurbishers/recyclers)

The fan type is "radial", EBM Pabst make an assortment of them.

Ebay has a pretty good listing.

They tend to be very expensive on ebay.

I found mine (I got 2 different-sized pairs) by constant, relentless ebay searching.

The answers to your technical questions could best be found in a EBM Pabst catalog.

Best,

-AC

You could build a water source heat pump to supply some of the heat, with the generator supplying the rest. Should be far more efficient than idling the "APU" purely for heat. Also, when connected to mains (maybe not often enough for it to really matter), the APU wouldn't have to run at all.

Ok, I've done a couple of hours of googling & reading about water source heat pumps. An Open Loop Water Sourced Heat Pump is of great interest now.

Alas these seem to be aimed at moderate sized houses or larger. The smallest I did find was a Dimplex SIH 4 ME (4KW) but it is listing at £3.5K/$6K. Several times more than a 5KW Diesel Water Heater designed for a Marine environment. The power use of the heat pump will need looking into carefully.

Also I have a feeling from my initial reading it would take 1KW.hr as an input (EG in a 4KW Heat Pump that needs 1KW electrickery), whereas a 5KW Diesel Water Heater would need 35-50 W.hr as an input (for the circulation pump & control unit aspects... IE nearly nothing). Power is a big concern as previously mentioned.

Still, DIY to the rescue? Do you have any more specific advice/pointers in this regard?

Cheers!

You might try the Homemade Heat Pump Manifesto

You should find a good bit of information there.

-AC_Hacker

Rather than run the APU at a fast idle just to get it making some heat, actually use it as a generator and make use of the power to run a heat pump, while still making use of the heat from the engine. In your situation, it wouldn't be too difficult to net more heat into the space than what was in the fuel to begin with.

There isn't an [propulsion] Engine(s) as you are assuming (normally, you'd be quite right).

Currently planned: There will be two 14KW PM DC motors for propulsion. 1KW Solar, 40KW Batteries & 5-8KW Diesel Generator (+ occasional 3.5KW Shoreline). It's an 'all' electric boat (well Diesel/Electric Serial Hybrid technically speaking due to generator - and the 5KW Diesel water heater previously mentioned).

Nice! How civilized!!

-AC

Then it would be a range extender rather than an APU, but same idea.

Assuming the generator is 30% efficient (diesels generally do better) and the thermal recovery system can recover 80% of the waste heat, the heat pump only needs to get a COP of 1.47 (EER of 5) to beat an ideal furnace. For comparison, a cheap window A/C easily does 9.7 EER or more.

Hello everyone,

I'm a relatively new ecorenovator. Concerning this site it is. I've been working on my house for a number of years now and probably considered a bit of a geek by many people, but it's nice to see I'm not the only one!!
I've read the whole thread from AC-Hacker about building a heat pump, a little in the conservation section and this thread. It took me a few days...
I have a house that's CO2-neutral (including the electric car BMW i3). The house was built in 1987 including a balanced ventilation system with heat recovery (1 cross flow hx). So it should be OK. But the efficiency I measured was approx 65%. This is only based on measured temperatures. So not including moisture effects. So in reality it could be a bit off the real value.
I thought about improving (or replacing) my system to achieve a better efficiency. However I'm also concerned about the AC-fans I have. To my opinion DC fans must be much more efficient, especially because in normal conditions (medium flow) my AC-fans run with a high "slip" (percentage of difference between the rotational speed of the fan and of the rotational speed of the electrical/magnetical field). This is achieved by a series capacitor.

But thinking about my centrifugal fans, I wondered about the fact that in this thread I almost all the times am reading about small axial fans. In my opinion generally the combination of hx, filters, ducting etc. requires a dp that most axial fans don't produce.

Of course I've seen the efficiency calculations (based on temperatures) in this thread and they sometimes looked impressive!
But I wonder if someone really did flow measurements. I fear that in many installations the efficiency might be OK, but the flow is just far below what's required. Normally in Europe we calculate these installations with 30m3/hr per person and some minimum values for toilet and bathroom.

Just curious about the measured flows. Anyone?

If you want to see details about our house and how we achieved CO2-neutrality, take a look at our site. It's in Dutch, but Google translate can help (although sometimes the translations are funny/odd).
The title means: No more energy bill. Here it is: geen energierekening meer: energieneutraal woonhuis fam. Kriegsman Ootmarsum - Rekening energiebedrijf 2013

Congratulations on CO2 neutrality!!!

You have achieved a goal that most of us haven't even allowed ourselves to dream of... and you have done it, very nice.

But as you surely know, a lot of improvement has happened since then, with ECM fans and improved HX cores, etc. I would check into what kind of HRVs are being used for Passive Houses. They seem to be at the cutting edge of this kind of thing.

Good point!

I did some experimental work that was posted on the DIY HRV thread, and Mike, the guy I was working with, happened to have a precision air volumetric measuring meter. They're really expensive and he was pretty lucky to have found one used, in good condition, and cheap.

In the DIY HRV thread also, there is a procedure described that uses very large plastic bags, and their volume is estimated and the time-to-fill is measured. I know it sounds very crude, but it should give you a good approximation of air volume rate.

-AC

If you want to do a proper measurement (including the duct losses), you should install plastic bags on all supply nozzles (in my case there are 5) and have someone with a stopwatch at each bag....
Otherwise you could only measure the hx + filters.
On the other hand... that's better than no measurements at all.

I had the opportunity to borrow a flow-measuring device that's intended to measure airflows from ventilationsystems (TSI Velocicheck including air capture hood).
In this way I was able to measure each separate supply nozzle and extraction nozzle and after that, I could adjust the nozzles so that incoming and outgoing air were really balanced.

Yeah, when I was working with Mike, he had a similar instrument, and we were measuring airflow from a duct opening. He measured at the edges and the center and various other places in between, and it was clear that the velocities were quite different across the opening. To get real volumetric accuracy, some averaging was needed.

The bag method takes care of those differences.

But if you only want to balance velocities, I suppose a center measure would do it.

-AC

I use one of these when it comes time to quantify airflow and changes. I does require some averaging.
http://www.amazon.com/General-Tools-...ords=meter+fpm
One of the biggest difficulties for diy systems would be btu measurement. I see variations in manufacturer's btu certifications on systems' output with the same condensing unit and different blower or coil options. Without the correct btu output you can't calculate seer or btu per watt.

My DIY HRV system completed
 

Hi people, it's been a while since my last post, after many months of hard work I finished what I call the first version of my complete DIY HRV home system. As I previously said I wanted full-house ducting with outtakes in the livingroom and bedrooms and intakes in the bathrooms and kitchen. That meant lowering 13cm the whole ceiling of the first floor, some 45sqm of drywall done in aprox 10 days work there... By the way I also installed new recessed LED lighting and an also recessed VPR motorized housing with motorized screen and HT sound system. I finished the first floor last August (2014) and the rest of the ducting by February of this year. The HRV is rocking since then and, even if the winter wasn't very cold this year, the inside comfort is superb! No more window opening, no more cooking odors on the second floor, no more steamy mirror while taking showers! Last but definitely not least, you get all that fresh air during the sleep, which is priceless.
Here are some photos:

First floor plan with duct project (orange return, blue supply)
http://ecorenovator.org/forum/attach...4&d=1431696473

Kitchen return boots - project

http://ecorenovator.org/forum/attach...8&d=1431697932

http://ecorenovator.org/forum/attach...9&d=1431697932

Boot construction:

http://ecorenovator.org/forum/attach...0&d=1431697932

http://ecorenovator.org/forum/attach...1&d=1431697932

Distribution plenums:

http://ecorenovator.org/forum/attach...2&d=1431697932

Demolition man! :D

http://ecorenovator.org/forum/attach...3&d=1431697932

Left: corridor supply hole, right: kitchen return and livingroom supply hole.

http://ecorenovator.org/forum/attach...4&d=1431697932

Twin boot (kitchen return and livingroom supply) project and construction

http://ecorenovator.org/forum/attach...5&d=1431697932

http://ecorenovator.org/forum/attach...6&d=1431697932

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<<<continued from previous post<<<

Twin plenum installed:

http://ecorenovator.org/forum/attach...7&d=1431699184

Kitchen boots installed:

http://ecorenovator.org/forum/attach...9&d=1431699184
http://ecorenovator.org/forum/attach...8&d=1431699184

Corridor duct:

http://ecorenovator.org/forum/attach...1&d=1431699184

Corridor duct installed on the left, VPR recessed motorized lift (DIY, of course!) and twin boot on the right, Santorini in the center :D :

http://ecorenovator.org/forum/attach...0&d=1431699184

Kitchen return ductwork:

http://ecorenovator.org/forum/attach...2&d=1431699184

Distribution plenums and drywall construction:

http://ecorenovator.org/forum/attach...3&d=1431699184

http://ecorenovator.org/forum/attach...4&d=1431699184

Cladding finished, this is the kitchen return hood:
http://ecorenovator.org/forum/attach...6&d=1431699184

And this is a finished view with the new lighting fixtures:

http://ecorenovator.org/forum/attach...5&d=1431699184

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<<<continued from previous post<<<

Grilles and filters:

http://ecorenovator.org/forum/attach...7&d=1431700022
http://ecorenovator.org/forum/attach...8&d=1431700022
http://ecorenovator.org/forum/attach...6&d=1431700022

Livingroom grille:
http://ecorenovator.org/forum/attach...9&d=1431700022

Corridor supply and mixing grille:
http://ecorenovator.org/forum/attach...0&d=1431700022

http://ecorenovator.org/forum/attach...1&d=1431700022

Bathroom drywall cladding:

http://ecorenovator.org/forum/attach...2&d=1431700022

Bathroom return stackhead:

http://ecorenovator.org/forum/attach...5&d=1431700022

Stackhead installed with grille:

http://ecorenovator.org/forum/attach...3&d=1431700022
http://ecorenovator.org/forum/attach...4&d=1431700022

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<<<continued from previous post<<<

Over the stairs return grille:

http://ecorenovator.org/forum/attach...7&d=1431700933

2nd bathroom return grille while checking air speed:

http://ecorenovator.org/forum/attach...8&d=1431700933

Kids bedroom supply grille:

http://ecorenovator.org/forum/attach...9&d=1431700933

Bedroom supply grille:

http://ecorenovator.org/forum/attach...0&d=1431700933

Supply and return chimneys construction (you can see the IKEA bowls I used as caps)

http://ecorenovator.org/forum/attach...1&d=1431700933

Roof installation:
http://ecorenovator.org/forum/attach...2&d=1431700933

http://ecorenovator.org/forum/attach...3&d=1431700933

http://ecorenovator.org/forum/attach...4&d=1431700933

Inside ductwork to the HRV (from bathroom and kitchen and to livingroom)
http://ecorenovator.org/forum/attach...5&d=1431700933

Bathrooms return plenum with spiraled tube attached to the HRV:
http://ecorenovator.org/forum/attach...6&d=1431700933


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<<<continued from previous post<<<

To the bedrooms PAL ductwork:

http://ecorenovator.org/forum/attach...7&d=1431701603

The beast is on!

http://ecorenovator.org/forum/attach...8&d=1431701603

Arduino control board. I used 4 DHT-22 temperature and humidity sensors, one for each flow, and 6 relays for the two motors (3 for each one, one per speed)
http://ecorenovator.org/forum/attach...9&d=1431701603

Arduino web interface control panel:

http://ecorenovator.org/forum/attach...0&d=1431701603

DIY ultrasonic humidifier (dedicated post in the near future :) )

http://ecorenovator.org/forum/attach...1&d=1431701603

That's all for now, hope you enjoy :thumbup:

What an awesome project!!
 

Amazing, inspiring project, and beautifully documented too.

Thank you for going to the trouble of posting it for all to see.

I would have to say, that I fear that the small holes you drilled in the outlet covers, might restrict the free flow of air, and may increase noise and energy cost.

Other than that, I am astounded.

Best,

-AC_Hacker

That is very impressive work! It looks great and to hear its functioning well is even better news. Thank you for sharing!

Thanks, glad to contribute.
AC, the covers are machined punched, the two small ones are shelves from the local IKEA store and the long one (kitchen) is custom made. There are more than 3200 ø5mm holes in it, which is more than enough for a single inlet. Besides, the whole ductwork is actually oversized as I used ø150mm (or equivalent when rectangular) for almost every branch, which could hold up up to 200 m3/h (118 cfm) within the safe range of laminar speed (that's 3m/sec) and thus virtually noise free. The actual flow of every branch is hardly 25 m3/h for everyday use, so I'm quite sure about having no unwanted turbulence.

Hi :) This thread is great. I've been looking at the Recair premade recuperators, they're really cheap. I saw Fornax has posted pictures but they seem to have disappeared, anyone know if they're still around somewhere? I'm a forum newbie so I don't have PM rights yet to ask Fornax for them.

Cheers!

Hi Tinco,

What disappeared? Recair or some pictures I posted?
In a message dating back 30-6-2013 I posted 2 links which are both still active. It looks like Recair is since aquired by another compagny, or changed it's name but Warmtewisselaar Webshop | Home is still working, and you can now choose between dutch/english on the site. That's the website I ordered the heatexchanger from. (Be advised that advertised prices are excluding VAT (21% BTW).)

Hi Fornax, a couple pages back I think there were supposed to be some pictures of the HRV you built that I was hoping to see. I found the recair site and was wondering how best to integrate it in a diy project.

I did post a few pictures in this msg http://ecorenovator.org/forum/35514-post433.html
Obviously there are several possible designs, depending on the amount of space you have and what fans you are using.

I am still using the HRV pictured in that message although now I would build it a bit different. The fans used there are AC-fans which use more electricity than DC fans (About 35W together in the lowest setting where DC-fans would use below 10W (a difference of 50,- a year on electricity)) and over time these fans started to make more noise. Alas it appears better fans are rather expensive.

Haha, now the pictures show up. I guess they just didn't work when I didn't have an account. Thanks!

What fan were you eyeing?

Hello!

This was great read. Still I was not able to read all the posts of this thread yet..
I am thinking of making heat recover at my flat (~60 m2/645 ft2)
Still I have only one hole in the wall where I could get air and where I can push air out aprox 0,15 m2 / 1.29 ft2 large. As it is 5 level building, it would not be so easy to drill just another hole in the wall. There would be needed different procedures and special permisions, which costs few hundred euros. :)
So I was thinking how about making recuperator which blows out air from flat for some time, heats the inside radiator and then blows air in taking back that from radiator. Therefore there would be only one tube out of the wall and only one tube inside my flat. So I could make fan to change rotation direction. Do You think such a model would be possible? What do You think would be best efficiency, if I could get best timing for in/out air blows? Are there maybe already blueprints for such solution?

You should be able to push and pull enough air through that size hole for the living space you describe. A typical clothes dryer moves 150 cfm through a 4 inch diameter duct. The hole you describe could move upwards of 1000 cfm before you would start hearing whistling or whooshing noises. Dividing that figure in half gives you 500 cfm of flow each way. This assumes a fairly short duct run to and from the hrv and the hole.

A quick Google search yields an easy formula:

"HRV Capacity in Cubic Feet Per Minute = 0.01(Sq footage of home) + 10(#Bedrooms+1)

Multiply your square footage by 0.01 and add the number of bedrooms in your home plus one times 10.
So, for a 1,700 square foot, three bedroom home:

CPM = 0.01 x 1700 + 10 x (3 + 1)
CPM = 57
The sizing number assumes that the HRV will be running 24 hrs per day."
(robbed from DIY Heat Recovery Ventilator Project)

So for your size of home, a constantly running hrv would only need to move around 50 cfm to be highly effective. A pair of 4 inch dryer hoses could easily handle this airflow. Beware of over-ventilating, especially if you live in a climate with high humidity.

Hey, thank You very much for the answer.
You made it more hopeful! :thumbup:

@KKNgroup - Have you seen the thru-the-window exchanger in this post?

@kostas you are good and all from this forum, in the last month I worked on a unit with recair heat exchanger RS160/500mm and I don't know where to put the sensors, if I put the sensor DHT22 in the duct, the readings are to small compared to readings from the outside of duct.
what place or setup do you recommend for me.
soon I will put a lot of pictures with my HRV made with bypass possibility inside the box, I must work on duct connections and door sealing, very close to finish the masterpiece :).

my last picture taken

Hi ferox, I see some great work there, looking forward to see what's coming up next!
I'm afraid I don't understand what you mean about the dht sensors. I placed them inside the case of the hrv, in a spot well exposed to the bypassing air. They worked quite well that way, only one of them died after 6 months of use but I had some spare units and promptly replaced it.