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Comment by _Nat_ | Hacker News Reader

Seems like the big drawback of the positive-pressure approach would be flushing the heating/cooling out, too (as you've said in the article). That drawback would seem to be proportional the flowrate of the positive-pressure airflow.

So what if you redo your experiment with lower positive-pressure flows? This is:

1. Keep the 280-m^3/hr purifier on the whole time.

2. Start with the 220-m^3/hr positive-pressure system running.

3. Wait for the particulate-level to equilibrate, then record the particulate-level and the pressure-difference (between outside and inside).

4. Reduce the air-flow of the positive-pressure system by, say, 20-m^3/hr.

5. Loop back to Step-3 while the air-flow of the positive-pressure system isn't negative.

With the objective to be to determine how low the positive-pressure system's flowrate can get while still maintaining its benefits, reducing heating/cooling losses.

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The system that I am having in place now is connected to our indoor air quality monitor and constantly regulates the fan speed of the PPS. By measuring the CO2 levels in the room, I can also detect when the room is actually occupied. This works extremely efficient and by playing around with the parameters can be optimized for cleaner air vs energy efficiency (or both).

So in a way it does exactly what you say and finds the ideal equilibrium to keep just the right amount of pressure needed.

Air to air heat exchangers will help a lot with energy loss.

Now that we have a CO2 meter, I am strongly considering wiring it to an air exchanger and having a PID controller just keep the house co2 below 600-800 ppm, and the pm 2.5 below 10 ug/m3.

> Seems like the big drawback of the positive-pressure approach would be flushing the heating/cooling out, too (as you've said in the article).

There are lots of enthalpy recovery systems on the market, some that can recover >75% of the 'waste' energy, though mostly aimed at larger customers. You need to do a cost-benefit analysis to see if it makes sense to spend the upfront cost.

Yeah, looks like you're right: [waste-heat recovery systems](https://en.wikipedia.org/wiki/Waste_heat_recovery_unit ).

Guessing that there are two main scenarios there:

1. A leaky house where positive-pressure causes flows to come out of various leaks all around.

2. A well-sealed house where positive-pressure causes flows to leave through a well-defined channel.

The first-case might be harder to recover heat/coolness from, as the (high/low)-temperature air might leak in a way that'd be harder to make use of it.

The second-case would seem to offer a stream of warmer/cooler air that could be used with a heat-exchanger or heat-pump or something.

To note it, well-sealed houses might have issues with relatively poor ventilation, making positive-pressure more desirable -- much like how the OP describes wanting to keep CO2-levels down with their positive-pressure system.

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