So, as far as I can see, this problem can be split broadly into two different areas:

1. Heat Exchanger (plus housing, condensate drainage, duct ports etc.).
2. Fans
3. Control system (fan balancing, condensation control, CO2 control, noise control, freezing mitigation etc.).

There are quite a few different possibilities for the heat exchanger and enclosure, and the fans - and the optimum solution for each project will vary according to quite a few project-specific factors, it should be possible to make a pretty good universal (and I would prefer open-source) modular control system.

I'm thinking of buying an off-the-shelf exchanger, and doing the rest myself.

Why?

At the moment, there are hundreds of companies worldwide making their own units (a few big players, and many small ones). They all write their own control systems (or don't have on at all, just "dumb" speed setting). This sort of reminds me of the market for "small" computers in the early 80s - they all came with their own software, and overall the cost was high and the quality poor. Unless you were a big customer, modification of the operating system was expensive (and possibly difficult / inconvenient, or even impossible).

Here are just a few of the features which I think we could all have with a good open source system, some of these are present in the best commercial designs, but none of them have all those features...

. Automatic fan speed balancing to overcome external wind conditions, duct resistances etc.
. Intelligent condensation control (based on dew point calcs)
. Speed adjustment to minimise energy usage and noise

Those would be an excellent start, and you can quite easily spend lots of money on units which don't do all of those. Once you have that, you could add in:

. Internal air quality control via CO2 sensors
. Freeze control and recovery
. Realtime efficiency calculation
. Error alerting (fan failures, efficiency loss etc.)
. Remote dampers or auxiliary fans
. Noise control (based on time of day)
. Multiple sensor options (built-in, or remote, wired or wireless)
. Filter / duct cleaning reminders based on volume
. Summer cooling (over-night heat exchanger by-pass options etc.)
. Decent user interfaces (control panels or Android, iPhone, Web) and data logging options

Some of the higher-end models have some of those features, but I bet that none of them have all those features, and if the software became good enough (and was correctly licensed), then commercial manufacturers (especially the smaller ones) may well even pick up the software and begin using it themselves...

Any thoughts (overly ambitious maybe? :p )

Tim.

They will a bit, but they'll also increase the cost (for a given volume of exchanger) and embodied energy. I believe that the limiting factor is the conductivity of the air, so an important thing is to get good turbulent air flow through the exchanger. Many commercial units use plastic, or paper based exchangers for this reason.

Yes, but that's still 80% less than without "heat-recovered" ventilation, and it's quite reasonable to get 90% efficiency or more at lower air flows.

There's a nice calculator to play with here which gives efficiency vs. air flow for one manufacturers' exchangers:

http://www.recair.com/recuperator_models.php

People need outdoor air to keep indoor CO2 levels under control, and also to avoid indoor pollutant build-up (the standard for UK schools is something like 10 litres of air per pupil per second or 1500 parts per million CO2 max daily average). We aren't well evolved to indoor living, and CO2 build-up does all sorts of odd things to our bodies.

At night, it might be reasonable to drop that figure to 5 l/s per sleeping person (e.g. 55 m³/hr == 32 cfm for 3 sleeping people). If your house leaks enough that you already get that amount of air in "by accident" (depending on wind speed), then you probably need to fix that before fitting an HRV...

Most speed controllable fans seem to go down to 10%. If you're shopping for cheap EC (electronically commutated == high efficiency, long life) ebm papst fans, there seem to be various available some are standard parts (i.e. ebm publish the data sheets), and some seem to be customer-specials (may be a bit more tricky to control).

I don't fully understand the ebm naming, but many seem to come in 4 different variants:

ending in "xyz / blahblah P" are PWM controlled (easy with arduino etc.) 0%, 10%-to-100% (i.e. probably) 0-9% not possible.

ending in "xyz / blahblah I" are controlled by a 0..5v (or sometimes 0..10v) signal (this is also possible with an arduino with a few extra components - many sample designs findable on the net) 10% speed minimum same as PWM.

ending in "xyz / blahblah T" are controlled by a thermistor in the air flow (either built-in, or user-supplied), dunno how far you can "turn these down", might vary by type. Can control these from an arduino too, but might require a bit more fiddling.

Most of the EC fans the market aren't speed controllable and just have a 2 supply wires (sometimes you can reduce them down to 70% speed by changing the supply voltage, but this is a PITA, and probably not worth the hassle - I think 70% to 100% is probably not very well suited to domestic loads, and a wide control range is probably better suited.

There seem to be a few cheap used "P" fans floating around from Sun servers, and also quite a few cheap "T" fans from Lucent kit (new and used).

Generally as far as I can tell, axial fans are generally the most efficient for low resistance set-ups. Centrifugal fans are generally the most efficient for medium and high resistance set-ups, OK for low-resistance too, but a bit less efficient and a less convenient shape. Mixed flow are a sort of hybrid between the axial and centrifugal - most efficient at intermediate pressures.

They do DC and AC supply ones.


Another possible option which I looked at were 12v DC "bilge" fans for boats. These are quite cheap, and you could control these fairly easily with something like an Arduino + motor controller, but most of them probably use "brush commutated" motors, which won't last as long, and aren't as efficient.

The larger standard computer case fans are also possibilities (14 cm etc.), and are quite cheap, but tend to be a bit less efficient, and need very low duct+heat-exchanger resistances. You can install two (or more) fans in series tho' (2 fans in series will roughly double the static pressure at a given air flow).

This is a small heat pump, it doesn't need a 16kW compressor! Since you'll have relatively slow airflow, then make the HP's heat exchangers large. Also, you won't be moving a terribly large amount of heat, plus the temperature difference is small, so you could probably get away with a compressor from a fridge or freezer. OK, not a 30W tiny fridge compressor, but a 150-250W compressor from a larger unit might suffice.

Going slightly off topic, in that drawing of mine I suggested that the intake path start with an underground heat exchanger to preheat the fresh incoming air, which should also lower the temperature differential between the two airstreams coming out of the recuperator.
Since building an underground HX isn't always possible, how about a solar collector instead? Imagine that the recuperator's fresh air enters through a vent in the wall. Now place a solar box in front of the vent (south facing insulated box with glass on top). If the sun is shining, then the intake air gets free heat, else it is the same as without the solar box. Similar to a solar air warmer for ASHP I once proposed.

Piwoslaw I am currently planning to use the terminal part of my propane heater's exhausting pipe as a pre-heater for my HRV (you can see some early pics here). When the heating is on the incoming air gains about 8 degrees Celsius, which is not that bad at all.
Connecting a solar panel is also a good idea, but you have to add extra fans due to pressure drop inside it. Keep in mind that a well constructed air panel easily arrives at high temperatures. If the incoming air temperature is higher than the out coming stale air it gets cooled by the exchanger. To avoid this a thermostat is needed in order to stop the stale air circuit and allow only the hot air to pump into the house.

^^ Yeah, I forgot to mention the thermostat by-pass. Also, The solar box would be removed altogether during warmer months.

I believe you need to scale the heat pump size way, way down.

I came across some European units that work as power-assisted HRVs and also help heat water. Their compressors were really tiny. As I recall, there was some information posted earlier in this thread about such a unit.

The smallest de-humidifier compressor I know of can be found in a 20 pint per day dehumidifier, and had a compressor of about 300 watts (about 3200 BTU).

Some of the tiny cube refrigerators have compressors about 125 watts, but their COP looks to be awful... But if you could find one cheap, it might be worth a try.

The little dehumidifiers are best for experimenting, because you already have the air-to-air HXs, and a useful cap tube. I doubt that you would want to use the fan though... you could do better with some of the fans that are currently being discussed.

An R22 unit is great because you can use propane, but then again, the R134a units use refrigerant you can get over the counter at auto parts stores. The R134a is not flammable, but it is a global warming gas.

If it were me, I'd go for the very smallest size de-humidifier compressor I could possibly find... see how it works out, you'll really learn a lot. Then scale it up if you need. But since you're only trying to salvage the heat in stale air, very little power is required... unless your house is quite large.

But all this HRV discussion is predicated on having a nearly hermetically sealed house, where mechanical ventilation is an obvious requirement.

-AC

A has been said, the air flows involved in heat recovery are relatively much lower than is typically needed for the size of heat pump which will be able to heat a building. You will also get increased risk of icing on the evaporator size, since the air will already be at 100% RH. Both of these may limit the usefulness of this design in many situations, but you'll need to do some maths to see if they will be a problem in your situation.

Maybe it'd be of more benefit for summer cooling? You can also use evaporative cooling on the exhaust air before you feed it through the exchanger, that way you get the benefits of evaporative cooling (cost), without the problem of increased indoor humidity (which cancels a lot of the benefits).

Tim.

Any idea what sort of COP the de-humidifiers achieve? Looking at this table:

http://ecorenovator.org/forum/conser...hanger-14.html

The efficiency of the best units seem to be about 4x those of the worst.


At first glance, I think that running the heat recovery ventilation part efficiently (and quietly) is probably going to conflict with running the heat-pump part efficiently. Having lived with a heat recovery ventilator in the past, and taking into consideration the way my house is used, I'm guessing that on average (during the heating season) the unit for my house is probably only going to run at an average of 50 m³/hr or so (a lot of the time there's no one in the house during the day, only a bit of humidity being generated by house plants, and maybe drying clothes in the "drying cupboard" which I'll place next to the HRV unit).

Playing with that recair calculator, if I build a unit to work at 300 m³/hr peak, but only run it at 100 m³/hr normally, then when it's running at the 100 m³/hr figure, it'll use something of the order of a quarter of the power to run the fans vs. the peak flow (which is a significant saving - maybe 60 watts), but the losses in the exhaust air will drop to about one eighth of the peak-flow amount (an even more significant saving - maybe 200 watts). The factor of 3 gain (from transferring only a third of the amount of air) is multiplied by the considerable improvement in the heat recovery core's efficiency which results from passing air through it more slowly.

So intelligent control software could be conservative about turning the fans up (if I get a bit of condensation on the windows occasionally, that's OK in many cases, so long as it doesn't sit around long enough for building materials to get damaged, and mould to start growing etc.).

Quoting Exeric from another thread:
To retrofit balanced ventilation with HRV to all the rooms in my house would be a nightmare. Over here all the walls are some sort of stone and all the floors/ceilings are concrete (Except the roof). In the near future you'll see some pictures.

Thursdaymorning I ordered the fans and some related parts. They could be shipped in less than 4 days so they arrived the next morning, that's timely indeed : -)
The package was short 1 of the 2 fans I ordered, which will be solved soonish.

Some pictures of the fans I'll be using, the Comair SOLO 44Y. Click the thumbnails.

HRV & Heat pump
 

Hi,

I just have a few comments about combining a heat pump and a HRV. I am with AC, I would think a dehumidifier is the easiest to hack. I will have to keep an eye out for one. Although they use more power, I think the benefit of the HXs is a big plus. When combined with the HRV, the heat pump wouldn't have to work very hard.

Timsmall brings up a concern of mine: "At first glance, I think that running the heat recovery ventilation part efficiently (and quietly) is probably going to conflict with running the heat-pump part efficiently." I think airflow is going to be critical, too much and the HRV isn't efficient, too little and the Heat pump isn't efficient. Although, Piwoslaw pointed out that a larger condensor/ evaporator would solve the problem of low airflow. Maybe it would be best to use the HXs from the dehumidifier with a small cube fridge compressor :confused:

Piwoslaws drawing showed the heat pipe and other people have commented on using a solar air collector on the inlet side. But I don't think you can combine all these things. Air heated by a solar collector will be cooled in the HRV. Air flow though the solar collector would also have to be compatible with the airflow through the HRV. You could still use a solar air collector, I just wouldn't run it through the HRV.


A heat pipe would have to be very long to get any noticable gain. Think of the length of heat loops in a geothermal system. If the heat pipe was long enough it might help some if the temperature outside is below 50* (general ground temp), then the heat pipe may warm the air some. But, if the air outside is, say 55-65*f, then the heat pipe would be cooling your incoming air when you still need heat.

I think it would be best to rely on the HRV to do what it is designed to do: bring the temperature up (as much as possible), then use the auxilary heat source (efficient heat pump) to top off the temperature so the air coming into the house is the same temperature as the air being pumped out of the house.

To make a system like Piwoslaw drew work, sizing and airflow will be critical, but I would also have to factor in the amount of noise it may make. I need to do more research. Or, I could probably "reverse engineer" a commercial HRV then try to match a dehumidifier to the flow of the HRV. Such is life. Thanks for the comments.

If you're talking about de-humidifiers as de-humidifiers, it's probably not very high. I know there are some people who claim to be using them as heaters, I would estimate the COP in that case to be greater than 1 and less than 2.

The COP of an ASHP depends greatly on the heat content of the incoming air, the heat content is partly because of it's temperature, and partly because of the water vapor content. If you use a heat pump to extract the non-water vapor heat (sensible heat) you can capture that heat, if you use a heat pump to condense the water vapor out, you can retrieve that heat (latent heat), too. Heat pumps do both as at the same time.

So, typically ASHP COP ranges from 2.2 to 3.7 average, with some higher COPs if the incoming air is warmer (like if the ASHP is used to salvage heat from warm, moist indoor air in a power-assisted HRV).

Best,

-AC

Talking about motors, what do you think about this one?
It is a dual centrifugal with these specs:
130 W

2300 rmp

Fan diameter 80 mm (aluminum)

Fan length 83 mm

450 m3/h

static pression 237 PA

Exit port: 50x108 mm

I could use just one for both fluxes. 130w seems a good compromise...

That motor is not a very efficient one since it's a shaded pole motor. Basically the cheapest motors around, lower end bathroom fans, kitchen forehead foggers, and very low end furnace motors use this type of motor.

I think that such a fan would make building your project pretty simple. In the beginning, simple is a very good thing. I'd say this is a good fan to use.

If your project works and solves your problem, then you might think about improvements. From my research, a fan that would lend itself to speed control is most desirable. I have seen Electronically Commutated Motors (ECM) that have a very good reputation for durability, are efficient, and lend themselves to control of speed.

Another good approach might be to look into HRVs that are similar to what you want to build. Download the manuals for the ones you like to see how they are built and get the parts lists, they will list the specifications for the fans.

Best,

-AC

ac_hacker yes, my thoughts exactly.
I saw those fans in a similar model that inspired my project. The advantage of this particular model is the price, roughly €65 which is very convenient. My only doubt is the air flow. A 50x100mm hose seems too narrow to do the work properly, but I guess I'll have to discover it by myself. Anyway, I can always get another pair in case one is not enough ;)
In that case I could control two separate motors for more speed if necessary, for a total of 260W

You might be over-thinking this thing a bit...

I don't know about your house, but my house is pretty much in balance when the air outside is 55-65 degrees, and just the additional heat generated by cooking, TV and very low power lighting keeps the place pretty comfortable.

A heat tube should be buried at least 3 ft deep (in our part of the world), more is much better. But during the days when the winter air temperature is hovering in the mid 30's to low 40's (as it does in the lovely Portland winters) the heat boost (underground temps here are around 54F) from an underground heat tube would be a very welcome addition to incoming fresh air temperature, before it hits the HRV.

And it's quite difficult to put a dollar value on the feeling of health and wellbeing that comes from breathing fresh, clean air.

Best,

-AC

kostas,

Are you really in Italy? I wish I was rather than in this wet gloom that is my fate in the wintertime.

Another good source for high quality fans that I discovered just yesterday, is electronics recyclers. I was down at such a shop yesterday, and saw a really choice high efficiency German ECM fan that would be absolutely perfect for a HRV project. Unfortunately, the fan I looked at had a bad bearing, but these things are used in large computer installations... only the best for large computer installations, you know. And when they upgrade, the whole system (fans and all) comes out and new systems go in (fans and all).

Best,

-AC

ac_hacker yeah, Italy, Venice to be exact. The problem here is summertime, with an average 60-70 % RH for 1-2 months... After nearly 15 years here did not get used to it yet! :(
I already checked the local electronics recyclers here, not that much unfortunately. And the thing is that you need two identical fans for an HRV in order to have a balanced system, which is not very easy to find there...
Anyway, speaking about the aforementioned fan, I can choose wether to buy a double one or two separate with identical characteristics (but, of course, doubling the power consumption, 130w each). I wonder what are the pros and cons..
Sure a system with two motors is more flexible, i.e. if I decide to swap the air inputs and outputs.

If it were me, I'd go for the the configuration that offers greatest energy efficiency. I try hard to reduce every watt, and I'm sure that energy is even more dear where you live.

Best,

-AC

Oh yes, you can say that! ;)

For comparison, those mixed flow second hand DV6224 fans which I mentioned (available at 25 euro or so each - I saw a set of four fans on US eBay for $30 I think), do the following at max speed:

89 watts

650 Pa (static)

700 m³/h (open flow)

http://img.ebmpapst.com/products/dat...224TDA-ENG.pdf

but they're speed controllable with an EC motor, so will go down to 10% speed giving 100 m³/h (open flow) and if similar fans which I've used in the past are anything to go by, they probably use less than 5 watts at that speed.

Have a look at the fan curve on the last page of the PDF.

Two fans are good not only for flexibility, but can also (potentially) reduce energy usage. During the nice warm spring and autumn there will be a few weeks or months when you won't really need the heat exchanger since the outdoor air will be in a good temperature range. Then you can open your windows and turn off the intake fan, using the other one as a house fan to remove stale air from the bathhroom and kitchen.

They are surely interesting, and moreover they could be easily controlled by the Arduino...
I can't see the noise figure, though.
Could you please pm me the ebay link?

Yes. In addition you can always use one of them as mentioned on post #245 ;)

I found another data sheet, which gives min and max values:

Full Speed:

69 dB(A)
89 watts
700 m³/hr (open flow)
5500 rpm

Min Speed:

29 dB(A)
2 watts
100 m³/hr (open flow)
800 rpm

So the 2 watts figure looks pretty good.

Careful, because I can't say for sure that the Sun variant will be able to go down to the minimum stated (they may have asked EBM Papst to change the firmware for them).

Try these searches (title and description):


DV6224/2tdp
371-0094
x4600 fan
papst 2tdp

I'm a new user so I can't send PMs! You should be able to track them down with the search strings above - PM me your email address if you don't.

Ops! Same for me, too! :D

Ok, I'll try to search better in the Bay ;)

I found this one in a fairly good price:
PAPST RG160-28/18N/13TDTV
(http://www.ebmpapst.us/allpdfs/RG160DC.PDF)

The curve is not very clear but it goes at least at 225 qm/h, maybe could do the job..

Thru-Wall HRV...
 

Here is another look at the problem...

This is a thru-wall HRV. It mounts on the wall and vents to the room, so no ducting is involved.

I thought it is very interesting how the assembly is layed out:


CLICK HERE for higher detailed illustration.

It's interesting how the air flow is incorporated into the design, also the use of an unusual fine wire heat exchanger.


Best,

-AC

Interesting variant, Ac ;)

In the meantime I finished the exchangers assembling.
I made one with coroplast sheets and another with aluminum, as I had already the material for both of them. Dimensions are 301x301x400mm each.
Here are some photos of the construction process:

I can't wait to see a side-by-side test of them! I'm very interested in the difference in efficiency of the two materials.

Piwoslaw I had already done some tests with the two versions earlier this autumn.
As I noticed there is no big difference by the two materials, the only one is that the aluminum core reaches it's working temperature faster.
But I can certainly say that the construction is way too harder than the coroplast, so I would definitely recommend the later.

Today I made the first of the two blowers. I used a new universal 135W motor for kitchen extractor fan. For the housing I copied the design of an old Rover 200 heating blower and I cut the sides out of plywood, then covered with aluminum tape. A piece of aluminum sheet covered the sides giving the final shape.
Tested it and it works great! ;)

Kostas, in those pics I see shiny foil and some foam. Are those for thermal insulation? Or is the foam to reduce vibrations and noise?

I used some strings of foam just to fill a slight gap between the motor and the case.
Lack of design I must admit!:p

I like your craftmanship Kostas, the aluminium is skillfully bend in shape.
Looking at the background in your pictures I get the impression you have a workshop with nice tools, which makes any job easier, I am not so lucky : -)

Did you cheat a little and continue with coroplast when you ran out of aluminium while building the HX-cores?

-----

Today I found the time to go to our DIY-store and get me some of the things I needed. This includes the wood (particleboard actualy) I need to house the heatexchanger core, and have it cut by them (which is free of charge, and straight).

Where in the US people often use OBS which is made of large chips here in the Netherlands we use particleboard with much finer woodchips, but not as fine as in MDF. The material is finished with a waterproof plastic, but the corners and bare cuts are vulnerable to moist, a point of attention.

Everything does fit snugly, and I sealed of every connection with an acrylic goop that is water- and weatherproof. Since the fans I'll be using are handy standalone machines that easily connect I kept the design of the housing for the HX very minimal. In the last picture you can see the enclosing with 2 HX-plates in it for an impression, I still need to saw the holes to connect the tubing.

Next comes the job to build the HX-core. It will be build from about 70 aluminum plates. Sealing will be made of selfadhesive PVC weatherstrips (4x9mm), these are compressable but do seal well. Since they are compressable I need to keep the individual plates separate by glueing a 3.5mm nut at the top and bottom centre.
It's not hard work but cutting 90m (300 feet) of weatherstrip to size and stick it in place will keep me busy for a while, but I guess it's not worse than glueing the same amount of coroplast strips in place.

I did have another minor setback. I planned to drill a hole in the floor of our shed and connect to the crawlspace under our livingroom. Our shed has no crawlspace, under the concrete slab is 60cm (2') of sand with no access. That means I'll have to reroute the ducting, which will make it longer than planned.

Anyway, the casing of the HX-cores is almost ready. The second fan that was missing from my order arrived quite fast. Most of the materials I need I have in the house so hopefully construction will go fast.

Perhaps I should tell you more about my home, in another thread. It's not a special house but it's obviously different than US, polish, italian, canadian and brittish houses.

Thanks, indeed having the right tools makes the work much easier. I grew up in my father's workshop, he was a carpenter, and since I was a kid I used to collect power tools. I don't have much room in my garage, but I managed to make it a good working place by the years.


And -yes you guessed it, I finished all the aluminum sheets!! ;)

If I can give you some advice, be careful with the PVC stripes. If they are sqiuzable that means that some of them could collapse by the overall weight .
In my case some stripes of coroplast eventually got smashed by the weight of 60 sheets over them...

I finished the cabinet that will house the HX-core.
Well, almost finished: I need to caulk the tubes where they pass through the holes and apply a few layers of varnish to the 2 bare faces of particlewood. But the constructing is done.

Kostas, you are right about the PVC weatherstrips being compressable, they are flexible foam.
When my order of aluminium sheets arrived I realized I was facing a designflaw. The package weighted 20.0kg (44 pounds).
So I went looking for some noncompressable spacers to guarantee an even spacing of the plates. I went for 2 nuts per plate, center top and bottom, put in place with thin doublesided tape. I thought a drop of glue was not a good thing since it's not guaranteed to be the same thickness along all the 70-ish plates.
Today I discovered the approximately 120cm of strip (4 feet) I'll be using per plate is more sturdy than I thought, it might be a problem to even get the plates close enough to eachother. I'll put the nuts in anyway, should the strip give in over time.

On the left side are OAI at the top and FAI at the bottom. Both the fans will be at the right side for FAO at the top and OAO at the bottom. The fan in the picture is just fitted into the hole in the cabinet and stays put. I'll secure it with some screws and caulk the connecting duct so it's airtight.

Okey, I see that we were working together today! ;)

You are doing a fine job, can't wait to see it finished. You've got a good feline companion, too!!
Is this a dual-hx housing? I see there is plenty of space inside.
I'd suggest you to use some aluminum foil to cover the inside of the box in order to create a useful UV barrier and save some more energy.
Beware of the water that will drip down the exchangers, as you said that kind of fiber board is not very keen of it. You could use a plastic collector underneath and drill a small hole for an evacuation plastic tube.

I tried to fix the first motor housing in place and drilled the exit hole. Was a bit tricky to calculate the optimal position, but i think I got it right.
This time I used some urethane foam sheets on the back side and neoprene tape for the vibrations :thumbup:

Great to see the progress of two HRVs!
 

I just wanted to say to both of you how great it is to see the progress of your two HRVs.

I just can't get over how miraculous it is to be able to easily communicate this kind of information and these kind of efforts to such distant parts of the world.

Very fortunate to be living in this age.

Best,

-AC

No, it's for a counterflow core with plates of 25x50cm (10"x20") and the core will be 30cm (12") thick consisting of up to 72 plates. The cabinet isn't that large, 90x30x30cm (3'x1'x1') on the outside.

I just removed the protective foil from the plates which resulted in an impressive stack of foil, which compressed well. (Plastic waste is collected separately and for free over here.)

In the 3rd thumbnail you see how the weatherstripping will go for the 2 different airstreams. The 4th shows how they will go into the cabinet. The remaining exposed aluminium will be roughly 23x48cm resulting in 0.11m per side per plate resulting in almost 16m2 for the entire exchanger (~170sqf).