[HN Gopher] DIY ventilation heat exchanger (2010)
___________________________________________________________________
DIY ventilation heat exchanger (2010)
Author : walterbell
Score : 133 points
Date : 2023-12-23 08:52 UTC (14 hours ago)
(HTM) web link (ecorenovator.org)
(TXT) w3m dump (ecorenovator.org)
| 0wis wrote:
| Interesting subject tackling two important home issues at the
| same time : ventilation and heat exchange. It seems like a way to
| get the best of both worlds. However, I do not know why this
| forum is relevant or interesting. DIY solutions are easily doable
| but is it really surprising ? I am sure people have done this
| with old fridge parts, as someone suggest in the last post. Yes,
| DIY can be cheaper but reliability is key for such systems. Size
| can also be key.
| notyoutube wrote:
| Reacting to your first point: As far as I know (western
| europe), heatpumps mostly are used to heat water to then heat
| your house, and renovating generally means reducing
| breathability of the house itself, which, combined with the
| temp difference, means condensation/mold problems. You then
| have to correct that by opening windows intelligently or
| installing air ventilation, and then a heat exchanger to not
| lose too much heat. Like you say, it seems to be a no-brainer
| then to instead combine heat pump _and_ ventilation, so that
| the ventilation itself works with a heat pump.
|
| The only counter-argument I have is that if all the heating
| were done using ventilation, you might have to live in a very
| windy house, but I feel like entirely decoupling the two is not
| the best solution to that problem...
| rocqua wrote:
| It makes a lot of sense to feed your ventilation output to a
| heatpump input for energy recovery with an air-source
| heatpump.
|
| But otherwise I think there is a lot of value in other forms
| of heating. Specifically in radiative heating. Floor heating
| is great for that, but other water-based systems are also
| possible.
| geon wrote:
| > if all the heating were done using ventilation, you might
| have to live in a very windy house
|
| Not an issue at all. A properly installed ceiling vent will
| blow air along the ceiling, where Bernoulli's principle makes
| the fast moving air stick to the ceiling until the speed
| drops enough for the higher density to make it sink gently.
|
| https://blog.swegon.com/hs-
| fs/hubfs/Bild4-1.png?width=1100&n...
| briHass wrote:
| There's also significant engineering calculations and
| guidelines/rules about the expected volume of air that is
| expected to enter/exit vents vs their size and grille
| restrictions. This is more to prevent loud airflow, but
| there's also charts for air distribution for room sizes.
|
| Now, most HVAC contractors go by gut feel/rules of thumb,
| but if you want to pay for it, a well designed system would
| never be 'windy' or noisy.
| ClumsyPilot wrote:
| > renovating generally means reducing breathability of the
| house itself, which, combined with the temp difference, means
| condensation/mold problems
|
| Look up Passivehouse standard, modern construction can make
| extremely effocient buildings, but it relies on the building
| being nesrly airtight, so it must have ventillation.
|
| 'Natural' ventillation naturally steals your heat, it's
| incompatiable with efficiency
| userbinator wrote:
| _Yes, DIY can be cheaper but reliability is key for such
| systems._
|
| If you know what you're doing (not hard to these days with so
| much information online), and depending on where you live, DIY
| HVAC can be far more reliable than getting a "licensed
| professional" who will attempt to overcharge for mediocre work
| or even scam you.
| Open_erv wrote:
| There was a period where I considered DIY for such machines
| impractical. I now think that to diy all the way through is
| impractical, the design process is too laborious even for those
| suitably skilled. However once the design is worked out it is
| actually pretty practical, with a 3d printer. You definitely
| have to own the printer, they charge way too much to have
| things printed at cloud services for some reason.
|
| I have pubished my STL files for an earlier version of the TW4
| energy recovery ventilator. It's totally practical to make your
| own with a printer, but it would take you a few days of labor
| time for sure to get everything working nicely.
|
| Reliability is very much on offer even with diy. In reality I
| have looked at many commercial units and they have serious
| reliability problems for long term like 5 years or more, and we
| should be planning for 50 years wherever building tech is
| concerned, imo.
| mnw21cam wrote:
| See also https://www.instructables.com/heat-recovery-ventilation/
| schiffern wrote:
| See also also https://youtu.be/w5sR-0oX1dg?t=184
|
| In this one the heat exchanger construction is closer to OP,
| with coroplast sheets glued together. However in a follow-up
| video, he says this was a bad idea for his humid climate.
|
| https://www.youtube.com/watch?v=LiptsaKmq80
| kragen wrote:
| heat exchangers are pretty important. does anyone have a summary
| of the high points in this thread?
| https://ecorenovator.org/forum/showpost.php?p=54888&postcoun...
| seems to be kostas's summary of their completed build, documented
| in more detail at https://diyvmc.wordpress.com/ and with an
| overview video at https://youtu.be/phIWQD5LAcA
|
| i have a couple of big unknowns about ventilation heat exchangers
| for houses, and i'm wondering if anybody knows the answers to
| these questions:
|
| - why is everybody using recuperators when a regenerator would be
| mechanically much simpler? i'd understand if preventing mass flow
| was important, but in fact this thread says that in some cases
| they build their recuperators with water-permeable heat exchange
| membranes in order to _facilitate_ mass flow of water, which is
| the main mass flow that a regenerator would introduce here. why
| don 't people use regenerators?
|
| - now that the price of solar energy has fallen so much, and in
| particular solar panels cost half what they did even a year ago,
| will house ventilation heat exchangers remain economical?
| nine_k wrote:
| I suppose that heat exchanger ventilation makes most sense at
| winter time. Not everybody lives in San Diego, a lot of people
| live in New York, Boston, Chicago, Seattle, etc, where a winter
| is a thing.
| genman wrote:
| Also during hot summer when outside temperature is hotter
| than inside - you don't want ventilation to bring in hot air.
| kragen wrote:
| i think heat exchanger ventilation makes roughly the same
| amount of sense whenever you're spending costly energy to
| change the temperature of your space, doesn't it? it works
| just as well to keep summer heat out as to keep winter heat
| in, and staying cool in summer can be just as critical as
| staying warm in winter, depending on where you live
|
| the main difference is that you can heat up a house
| (inefficiently) with a nichrome wire or a gas burner, while
| cooling it requires considerably more elaborate equipment
|
| but if electricity costs 2C/ per kilowatt hour and daytime
| electricity is free, will the savings of a heat exchanger be
| enough to pay for the device?
| spockz wrote:
| Electricity here is EUR0,30-0,40/kWh after tax.
| (Netherlands) (For fixed contact, dynamic contacts have
| bigger variation). That makes it way more interesting to
| save on energy. Although getting solar panels is still the
| fastest investment. Heat pumps typically have 10-15years
| payback time, especially now they are insanely overpriced
| due to Ukrainian-Russian war and climate goals increasing
| demand and lowering supply.
| kragen wrote:
| so when electricity costs drop by 15-20x the payback time
| will be 150-300 years?
| marcosdumay wrote:
| The temperature difference most home heaters work on is
| much higher than the one most home coolers work on.
|
| Using a regenerator to get 5degC of cooling back with some
| 30% of efficiency probably won't be cost-effectice. But if
| you have to heat by some 30degC, the numbers change a lot.
| nine_k wrote:
| Winter has much less sunlight, so powering a heat pump via
| solar panels + moderate battery becomes much harder. It's
| no longer mostly free.
| Open_erv wrote:
| You can understand quantitatively how this goes for different
| areas using Heating degree days and Cooling degree days,
| factoring in latent heat in both cases, ideally. There are
| calculators for this. I made a spreadsheet on my website
| www.openerv.ca that shows some of how to reckon this, there
| are links in there to get data.
|
| In Austin, texas, I think you got quite a bit more energy and
| money saved per year from avoiding cooling costs, but in
| Ottawa, Canada, you save about 100x as much in winter as you
| ever could in summer.
| schiffern wrote:
| >why is everybody using recuperators when a regenerator would
| be mechanically much simpler?
|
| They exist, search for "ductless HRV."
|
| They're simply a small fan that reverses every few minutes and
| a heat storage material. They also have wireless ones that
| coordinate the fan direction between them.
| kragen wrote:
| thanks!
|
| don't you need at least two fans and two chambers of heat
| storage material?
| schiffern wrote:
| That's how the wireless kind works. One unit blows in while
| a second identical unit (theoretically located across the
| house) blows out, and they switch roughly every minute.
|
| This balances the airflow, so you don't get non-regenerated
| (or more accurately, _less_ regenerated) airflow
| "somewhere else" like you do if you use a single unit.
| "in thermal regenerators, the hot and cold fluids pass
| through the same channels in the packing, alternately, both
| fluids washing the same surface area. In recuperators, the
| hot and cold fluids pass simultaneously through different
| but adjacent channels."[0]
|
| So these regenerative-type HRVs alternate the flow
| direction of the air, using the packing material as a
| thermal "battery" to warm the incoming fresh air from the
| outgoing exhaust air.
|
| While they are indeed simpler, my understanding is that
| they don't really perform well. There's no humidity
| recovery, the CFM is too low, the cheap units don't do any
| active pressure balancing, you can't continuously exhaust
| from bathrooms/kitchens, and the lack of net flow to
| distribute air throughout the house means you're mostly
| exhausting the fresh air you just brought in. Not great.
|
| If you're going cheap, skip the regenerator-type and the
| HRVs altogether and go straight to a jury-rig ERV.[1]
| Though again, ideally you can run flex duct (or temporarily
| on the interior, even just dryer hose) to pull exhaust air
| from the opposite side of the house, and specifically from
| bathroom/kitchen areas.
|
| However, first you should test your CO2 levels and/or do a
| blower-door test. Most buildings aren't tight enough to
| need an ERV anyway!
|
| [0] https://www.thermopedia.com/content/1087/
|
| [1] https://www.youtube.com/watch?v=CnLwJxCbxfM
| mrspuratic wrote:
| I've just installed a pair of these standalone units on
| opposite sides of a mostly open-plan 40m2 ground floor. They
| can run in intake/exhaust/cycle modes, and be paired as
| primary/secondary for contraflow.
|
| Too early to see energy benefits yet, but one thing that
| /really/ helps already is kicking both units into intake when
| cooking on the hob with the hood fan extracting. I should
| probably finish that hood sensor (looks at sensor sitting on
| desk).
|
| In trickle/night mode the rated performance is "up to 90%"
| (at 1.2W and 15m3/h in unspecified test conditions). These
| ones require a 165mm diameter hole, so the heat exchanger
| cross section is ~2.7 times the 100mm version, and presumably
| more efficient.
|
| I also installed (refurb, old house) a recuperative MHVR
| upstairs. This type has two fans for separated permanent
| intake and exhaust channels. The alternative in my country is
| knocking 7000mm2 holes in the walls (aka passive
| ventilation). I have to meet various building requirements as
| a refurb to qualify for energy upgrade grants.
| schiffern wrote:
| > one thing that /really/ helps already is kicking both
| units into intake when cooking on the hob with the hood fan
| extracting
|
| Not sure how much good regeneration is doing[0], but it
| sounds like it put a band-aid on your problem of inadequate
| make-up air for the vent! :D
|
| Do these standalone units recover heat only (HRV) or heat
| and humidity (ERV)?
|
| [0] https://news.ycombinator.com/item?id=38743885
| mrspuratic wrote:
| I have no external heat recovery system, so yes it's
| exactly zero while I'm cooking - but a reasonable way to
| maintain air quality in an open plan, one of my goals.
|
| The house also has new external wall insulation and other
| upgrades, so it's rather more airtight than before
| (though not formally tested just yet). Otherwise they run
| in synchronised cycle mode for heat recovery and air
| movement.
|
| I'm not well versed in all the subtleties of theory and
| current technology, but I don't think regenerative and
| true ERV go together. If condensation forms in the unit
| on the exhaust cycle I'd guess does contribute a little
| to the recovered heat?
|
| These units are BSK Zephyrs, with one heat mass component
| (ceramic honeycomb) and one fan inline in a telescopic
| duct. To prevent condensation issues they are fitted with
| a 2deg slope outwards, and a humidity sensor with
| settable thresholds to purge high humidity internal air
| at full rate (equivalent to about 1.2 air changes/h for
| me).
| Open_erv wrote:
| They all are capable of doing so under some circumstances
| with limited efficiency, because as the air exits the
| house and cools down at some point water condenses out of
| the air onto the regenerator media. Then it evaps again
| when flow reverses.
|
| However if you want maximal efficiency you want to add
| some zeolite 3A adsorbent, which you can sort of do
| yourself I am pretty sure. You just put some through a
| coffee grinder, put the regenerator in a garbage bag with
| it and shake it to get the powder inside the regenerator.
| It's not idea but it'll certainly help. I tried this with
| a thermal wheel of comparable size with silica gel and
| measured the result with AHT10 sensors and it worked
| pretty good actually.
|
| Zeolite lasts longer but you need more. Obviously you
| gotta try not to get the powder everywhere by getting
| excess off etc.
| mrspuratic wrote:
| Interesting. With EWI and internal insulation the
| telescopic duct is nearly maxed out as the total wall
| thickness is close to 500mm, but 50% of that is empty
| space. I though I might be able to get a secondary heat
| mass into that in future.
| andbberger wrote:
| commercial systems often use rotary regenerators
| jnsaff2 wrote:
| This dude built their own and got bad mold problems
| https://youtu.be/LiptsaKmq80?feature=shared
| keep_reading wrote:
| Exactly my concern... Just buy the Aprilaire 8100 and don't
| risk mold...
| zug_zug wrote:
| Fascinating video. There was a comment on his video asking
| "Wouldn't this introduce the same amount of humidity/mold as
| opening a window?"
|
| Curious if anybody has any more insight.
| geon wrote:
| There could be some issue with condensation. The moisture
| from the indoor air could get trapped and leak.
| aifooh7Keew6xoo wrote:
| I think the issue is that when the heat exchange occurs one
| way, the HRV is effectively a condenser.
|
| Moisture builds on the heat exchange surfaces of the heat
| exchanger, particulates, spores, etc. in the air deposit
| nutrients and viable life in the crud, it thrives and
| multiples right into the incoming airstream for your
| residence.
|
| When the window is opened the air mixes without a surface for
| condensation and there's much less immediate deposition so
| there's not an enriched medium to sustain accelerated growth
| entirely in the air stream, but it still probably occurs to
| some extent in a more diffuse manner that produces a
| significantly lower ambient spore/toxin/particulate load
| thadk wrote:
| Wow, even just that bit about mold being able to colonize a
| dehumidifier without its own MERV/HEPA filter is an important
| and hard to realize insight.
| schneems wrote:
| Ive been deep down the HVAC rabbit hole. You really need 3
| separate systems to do it right:
|
| - ERV - Dehumidifier - HVAC
|
| And basically no regular installer does it right. Lots of
| efficiency nerds over at Green Home Builders, subscription
| required.
| samstave wrote:
| Should throw in a UV bath as well - to kill any airborne
| spores/other critters.
| schneems wrote:
| It's been a long time since I looked into it, but IIRC the
| exposure time doesn't make sense in a duct. RealSexyCyborg
| talked a lot about this during the pandemic. Though that
| analysis was limited to the Covid virus.
|
| Also to watch for: Some solutions produce irritants like
| ozone. Not to say they aren't appropriate, just that they
| don't come risk free.
|
| It would be a good question for that forum for sure.
| leoedin wrote:
| It seems that the problems he had were in summer. There's many
| climates where HRVs are only really needed in winter - in which
| case those problems wouldn't happen.
|
| Basically, as long as the outside air is drier than the inside
| air, an HRV will work well. The moment the outside air contains
| more moisture, ventilating will just drive up the humidity of
| your space - causing many issues.
| walterbell wrote:
| For winter WFH in a rental, there aren't many commercial options
| for energy efficient ventilation to keep CO2 at reasonable levels
| for cognition. DIY HRV with coroplast can be customized for small
| spaces.
|
| For those with more room, an exhaust duct can transfer heat to
| cold intake air, https://www.loudawson.com/17884/how-to-build-
| air-cross-flow-.... Commercial units start around $1K+,
| https://www.sylvane.com/search/results/?keywords=hrv.
|
| One can also combine a DIY enclosure with commercial parts, e.g.
| crossflow, https://www.aliexpress.us/item/3256801499168685.html
| or ductless,
| https://www.aliexpress.us/item/3256805773352155.html.
|
| ERV pros/cons and review of $500 Panasonic FV-04VE1 ventilation
| fan: https://doctorpapadopoulos.com/in-depth-advantages-and-
| disad... & https://www.amazon.com/Panasonic-
| FV-04VE1-WhisperComfortTM-V....
| TheWoolRug wrote:
| In a rental where you can't cut through the walls introduces
| challenges. I wonder if anyone has created a DIY window unit
| that incorporates a "ZEHNDER COMFOAIR 70" which is a small
| contained HRV unit that has c02 detection and can ramp fan
| speed to match co2.
|
| https://www.smallplanetsupply.com/small-planet-blog/2020/6/6...
| andbberger wrote:
| you can hookup the panasonic unit to a window manifold for a
| portable AC and put some insulation board over that. that is
| the only reasonable solution I have found for the states
| aifooh7Keew6xoo wrote:
| I've had good success adding various utility and
| ventilation feed throughs in rentals with sliding glass
| door inserts, including large ducts for various HVAC
| experiments.
|
| I start with a board and cut/slot it so it fits neatly into
| the top and bottom tracks, then I move the latch receiver
| to the board, zip a few screws through the board where the
| holes won't be noticed.
|
| The glass door opening becomes a bit narrower, and I can
| cut as many holes as I want in that little bit of wall.
|
| If it's painted white it usually ends up looking better
| than most of the corporate maintenance work on the
| building.
| walterbell wrote:
| Bionaire Everfresh (circa 2005) $150 window HRV was
| discontinued, https://www.youtube.com/watch?v=OcVowAsYVI4
|
| $300 option from Alibaba,
| http://mistersustainable.blogspot.com/2021/08/another-
| mini-e...
|
| $700+ options, https://old.reddit.com/r/hvacadvice/comments/w
| dl0mn/do_windo...
|
| OpenERV design (writeup pending), https://x.com/open_erv
| sarchertech wrote:
| The CO2 cognition studies are almost definitely wrong. The
| military has done numerous studies over the decades with much
| much higher CO2 levels with none of the reported cognitive
| results reported more recently.
|
| The CO2 cognition studies show huge results. It's virtual
| impossible that none of the military CO2 studies would have
| picked this up with much higher CO2 levels.
|
| Also navies the world over have been running submarines for
| decades with astronomically high CO2 levels with no reported
| cognitive deficits.
|
| Whatever these recent CO2 cognitive decline studies are
| measuring it's not coming from CO2.
|
| One of the commonly citied cognitive decline studies shows a
| 50% reduction in cognitive ability at 1,400ppm. Submarines
| routinely operate at much higher levels and there was a study
| done where they exposed subjects to 40,000ppm for 2 weeks with
| no measurable cognitive decline.
|
| Here's a good summary from an old HN comment
| https://news.ycombinator.com/item?id=19863319
| JoshGG wrote:
| Hi. It would be interesting to read these military studies
| could you provide some citations or links?
|
| Are they published in reputable journals?
| sarchertech wrote:
| If you read the comment thread I linked to, you can find
| links to most of them.
|
| The real kicker for me is how absurdly high the effect is
| in the recent studies. You should basically see A students
| failing tests when the teacher closes the window.
|
| You should see huge swings in standardized test scores
| based on building ventilation.
|
| Companies with good ventilation, should absolutely dominate
| their markets.
|
| And nuclear submariners operating at 10,000 ppm should
| basically be non functioning if there is any kind of dose
| dependent effect (which the studies in question say there
| is).
| porkbeer wrote:
| Reminder that the military held that 4 hours sleep was plenty
| for a century, and had data to justify it.
| jorvi wrote:
| Yeah, I'm usually a very scientific man deferring to
| studies over personal feelings, but I can literally feel
| the mental fog clear up by the minute if I open a window on
| the afternoon in my study/work room after forgetting to do
| so in the morning.
|
| Hell, if I have a day where I am quasi-forced to spend most
| of it in musty rooms, I get a guaranteed headache.
| sarchertech wrote:
| There are so many things other than CO2 that can affect
| your feeling of mental fog. In addition the placebo
| effect is very very real.
|
| ISS astronauts are routinely living in a 5000ppm
| environment. If the size of the effects of these studies
| were real, they'd be noticeable.
|
| The most commonly cited study shows that 1400ppm cuts
| basic decision making ability by 25% and complex decision
| making ability by 50%. The study also shows a dose
| dependent response.
|
| So how are people routinely operating at nearly 5 times
| that level for weeks at a time with no noticeable
| decline?
|
| Results this large should by very easy to detect by
| simply measuring the CO2 levels at multiple SAT test
| taking sites and comparing scores.
|
| Even without looking, an effect this large is the kind of
| thing that would jump out at the College Board or any
| other standardized test creator anytime they're looking
| through their data to normalize scores or detect
| cheating.
| jorvi wrote:
| Here in The Netherlands for classrooms we have
| regulations that aim for a classroom to stay below 950ppm
| CO2. I think almost every high school kid can remember
| how drowsy a full, poorly ventilated classroom would get.
|
| Like I said I'm usually a scientific man but this is such
| a basic thing that anyone with any daily life experience
| would immediately recognize this 4000ppm (or whatever) as
| wrong.
|
| Humans are also quite sensitive to noticing when a room
| is "stuffy", so, yeah.
| maxerickson wrote:
| What's the typical temperature change associated with
| opening the window?
| cameronh90 wrote:
| Stuffiness is mostly a function of humidity.
|
| The problem with these casual discussions about CO2
| levels is they don't control for other factors. Opening a
| window definitely wakes you up, but is it the cold breeze
| or the CO2?
| sarchertech wrote:
| As far as I know the army said (and still says) 4 hours is
| enough short term in the field not routinely.
|
| If you're saying they suggested soldiers only need 4 hours
| of sleep long term, do you have any citations for this?
| Links to the studies they used to justify it.
|
| Because you can read the studies on CO2 and judge the
| methodology yourself.
| a1o wrote:
| Wtf are the Ads that replace the images attached to the forum
| posts?
| zug_zug wrote:
| Love the idea. Curious if there's any maximal theoretical
| efficiency. It seems to me that if you had a wide pipe with a
| narrow pipe inside (each going different directions) that you
| could theoretically have a system that transfers heat with no
| loss.
| upofadown wrote:
| You can in theory extend the length of a counter flow heat
| exchanger to get whatever efficiency you want. In practice,
| such a long heat exchanger would transfer significant amounts
| of heat to/from its environment. So then you are limited by how
| well you can insulate things.
| Open_erv wrote:
| This is approximately correct, except for one big problem
| with counterflow exchangers, which is frost. Even the
| membrane types still frost up. What you really want is a
| regenerator, either a thermal wheel or a fixed matrix
| regenerator, if you really want maximal efficiency. And it
| should be what they call the total sorption type, so it has
| some adsorbent in it. Even then the latent efficiency could
| be improved with a better adsorbent, the industry standard is
| zeolite 3A. It's good because it lasts. Silica gel becomes
| slowly inactive as it adsorbs other stuff that clogs the
| adsorptions sites basically.
|
| But the adsorbent only starts adsorbing at about 60% RH. So
| in some cases that actually leads to efficiency loss,
| compared to some kind of ideal adsorbent that adsorbed at any
| differential.
| doctorhandshake wrote:
| Dang. Read a comment in this discussion pointing out that an
| always-on ERV would work well in bathroom / laundry. I just
| installed a Panasonic ERV for a whole (~500sq ft) space and a
| Panasonic whisperquiet vent fan turned down to about the same CFM
| as the ERV in the bathroom as well. Missed opportunity to
| simplify, consolidate, and make more efficient the necessary
| moisture control in the bath by solely having the ERV there.
|
| GOLogic homes[1], IIRC, use a ducted ERV with return from bath,
| laundry, and kitchen, and supply to bedrooms.
|
| 1 https://www.gologic.us/
| scotty79 wrote:
| Shouldn't it also recapture moisture as well?
| Open_erv wrote:
| I'm the OpenERV guy. It's been a long road and it's not very open
| source any more I'll admit, however I did publish a bit
| Wikifactory article with all the cad etc. for a quite efficient
| window mount unit. I now have the know how to boost the flow
| through that thing by 2.5x or so so it could actually be a viable
| product/machine. However it's not a good business proposition.
|
| There is a whole class of energy recovery ventilators called
| decentralized, ductless or sometimes push-pull which are quite
| amenable to DIY. All you need is a good reversible fan and the
| regenerator and a pipe.
|
| I have shared elsewhere how to 3d print a regenerator. I use a
| 0.3 mm nozzle and it takes about 24 hours to print a regenerator
| that can do about 45 cfm at about 80 percent sensible efficiency.
| Basically just take a cylinder in Cura of the desired diameter,
| and use lines infill, no top layer, no bottom layer. That's
| basically it. Make the lines as thin as you can and the line
| spacing as small as you can while getting the desired airflow.
| About 2.7 mm on center spacing was about right for me and a
| typical fan with 6.5 mm stall pressure. The operating point was
| about 3.5 mm h2o and 45 cfm at maximal fan power.
|
| These devices do capture some water vapor during cold weather
| because the water vapor condenses on the heat exchanger then re-
| evaporates.
|
| I have tried sprinkling zeolite and silica gel in there to get
| good latent heat recover as well and it seems to work pretty
| well. You don't need much, only about 5 grams of silica gel, more
| for zeolite 3A molecular sieve.
|
| I have built two window mount units. One for myself, the mega
| sized one, which there are pics of on my twitter (@open_erv) and
| also one for my friend Alex, whose landlord wouldn't let him use
| it, so I sold it for the cost of the parts.
|
| It took forever to sell that thing even at the cost of the parts,
| so clearly window mount units are not a great business
| proposition. Also for other reasons, mostly people don't think of
| them as long term propositions so they aren't willing to amortize
| the cost of manufacturing a good machine over long periods.
|
| There is one called the purifresh, for windows too.
|
| The ductless models for houses include the lunos e2 for about
| $1800 CAD and only 25 cfm, and the blauberg Vento (there is
| another related one called Twinfresh), however I don't believe
| their noise or efficiency claims, and I have investigated.
|
| There are many cheap chinese knockoffs and some of them aren't
| too bad Holtop makes one. But mostly they are very poor.
|
| Ultimately I would like to make a hackaday or something that
| explains how to do all this, with a raspberry pi pico etc. Also
| an anemometer based on thermistors and the hot wire technique is
| useful to regulate flow, any extra flow in either direction hurts
| efficiency.
| aurizon wrote:
| A number of youtubes pop up.
| https://www.youtube.com/results?search_query=DIY+recuperator
|
| and the goog has a few more.
| https://www.google.com/search?q=DIY%2Brecuperator&rlz=1C1CHB...
| symlinkk wrote:
| Why is HN obsessed with air quality?
| serpix wrote:
| Commercial units coupled with a heat pump rival ground source
| heat pumps at a massive 4 - 5 COP. They even heat water and can
| take in solar heat piping.
|
| https://www.nilan.fi/tuotteet/poistoilmalampopumput/vgu/vgu-...
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