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Comment by frognumber | Hacker News Reader

I have air filters in all my rooms. I guess my questions are:

1) What should I do to get up to PPS? Should I just run a tube to their inlets through my window?

2) How is heating / cooling handled? The weather here swings wildly. I'd be reluctant to pump hot or freezing air in. Might work well in spring / fall which are peak allergy season, though.

3) What's a good way to monitor air quality on the cheap?

I'm looking for opinionated recommendations.

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1) The first DIY PPS that I built used a small duct fan drawing air from outside and pushing it through a hepa filter to the inside. It is important to use duct fans as you need to create air pressure more than air flow and box fans are not built to create the amount of pressure required.

2) Ideally you get a PPS system with a heat recovery unit. Also important is to have the PPS demand controlled based on an indoor air quality monitor that measures PM and CO2 and then only pushing in the right amount of air to meet your target values for PM and CO2. This way you can save a lot of energy costs and temperature differentials.

3) Thanks for asking ;) We maintain popular open source air quality monitor kits that are very easy to assemble and use industry grade sensors [1]

[1] https://www.airgradient.com/open-airgradient/kits/

I was looking for something like this.

Friendly note: "Join thousands of makers builing their" that's probably meant to be "building".

Thanks. Fixed.

I've been looking for an inexpensive PPS with heat exchanger that fits in a window (preferably an Andersen window, the kind that opens sideways, but maybe that's too much to ask). Since there don't seem to be any on the market (for any kind of window) I'm working on a design of my own. I think that two CPU coolers connected by their CPU plates with one pushing air out and one drawing air in would make a cheap heat exchanger. Then possibly running a large hose from the outflow of that to the air intake on a small HEPA air purifier would create a simple, cheap PPS. I know the pressure would not be high inside the house, but it would be a cheap way to introduce fresh air without losing heat/cooling and would help create a small positive pressure, without having to cut big holes in the walls.

CPU coolers are tuned for 300 watts cooling at a delta of 60ish degrees centigrade (100ish Fahrenheit).

You'd be operating at a much lower delta, split over two coolers. At best, the transfered power would scale with the delta, due to tuning it might scale worse.

I think you might be better off just skipping the heat-pipes of cpu coolers and using aluminum plates positionned in both airflows. CPUs need heat-pipes because the heat source is sooo small. Here your heat source will be much bigger, especially in terms of surface area.

Interesting, so in Winter, say the outside temp is 20F and inside temp is 69F, that's a 49F difference. In Summer, say the outside temp is 85F and the inside temp is 68F, a 17F difference. Maybe I'd get at best 50% heat recovery in the Winter and 25% in the Summer? That's a lot better than no recovery. I like the aluminum plate idea, maybe two big heat sinks with long fins attached back to back with the air blowing through the fins would work better and be cheaper. I like the fact that the CPU coolers are somewhat plug and play though, the fans are already integrated and power supplies are easily available. Both approaches are fairly easy and cheap to try. Wikipedia offers some insight on heat pipes:

https://en.wikipedia.org/wiki/Heat_pipe

So what is the working temperature range for CPU cooler heat pipes? Though they maybe be optimized for 100F temperature difference, CPU's also don't always run at full speed and maximum power. So perhaps CPU coolers would still be useful at lower temperature differentials (and lower absolute operating temperatures.)

> I like the aluminum plate idea, maybe two big heat sinks with long fins attached back to back with the air blowing through the fins would work better and be cheaper.

That's not quite what I meant. I effectively meant: just make one big, wide heatsink. Then have the intake run through the left side of the heatsink and outtake through the right side. No 'heat transfer between the heatsinks' needed.

Hmmm, there would still need to be heat transfer inside the heat sink from one side to the other via the bottom plate. Maybe that would still be more efficient than the transfer via a larger contact area between two heat sinks back to back? Not sure...either would probably work. What I can build might depend on the geometry and size of the heat sinks that are easily available. One big heat sink would make construction a little easier.

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