[AC_Hacker]

Steve

Thanks for the chip idea, but...

Originally Posted by stevehull

...Proportional control for an HRV (or ERV) is clearly overkill...

I'm sorry Steve, but it is not 'clearly overkill' at all. In a small air volume, proportional control would be much more comfortable, and unobtrusive.

About four years ago, I graduated from an on/off gas central forced air heating system to proportional controlled (AKA: inverter technology) mini split heat pump, and the civility and comfort of a proportional system is so unquestioningly superior that I'm just not interested in going back.

Those mini splits really have set a higher bar, not only in comfort but also in economy. It's just amazing how many tiny transistors you can cram into a tiny space nowadays... and what you can do with them.

I already have an Arduino clone (Teensy) that I plan to use, and if I understand it correctly, it can function in the same way as the IC you suggested. It also has analog-to-digital built in and PCM built in, and the capacity to handle another sensor (humidity) or two.

Originally Posted by stevehull

...AC has a good sensor and it doesn't respond to humidity and temperature as do many CO2 sensors...

The sensor I'm using in my controller is just capable of measuring CO2. But I have a borrowed sensor that I have been using just to monitor my environment, and it does read temperature and humidity and CO2. The measured levels of temperature and humidity are very stable. I imagine humidity will change once I get the HRV working, and I plan to incorporate a humidity sensor into the design.


Just to help guide your thinking, the HRV core that I have is identical to the one used in THIS UNIT.

In fact I bought mine from a former US affiliate that still had one left in stock.

The favorable economic operation of this unit, and the size of the house that it is meant to service is very attractive to me, because it approximates the size of my own house. I realize that my house is on the small size... but I do plan to expand the conditioned area, but not to the whole 700 sq. ft.

So here is a description of the controller that the Irish engineers came up with... hopefully, a similar controller can be developed. I mean, they can't be that much smarter than us, can they?

...the smart controls of the system monitor the temperatures of the 4 air-streams in the unit. The system will always run itself to maintain the highest level of efficiency while ensuring CO2 and humidity levels are regulated using sensors for each. When CO2 reaches 530ppm or humidity reaches 40%, the unit automatically slows down to trickle speed until levels become higher again. At 50m3/hour, the breathing window emits just 25dB of sound, while at high-speeds of up to 150m3/hour this increases to just 40dB. This is normally indistinguishable from normal household background noise. Breathing Window. The future of Passive House ventilation.

Cross ventilation above and beneath doors is crucial in all Passive Houses with ducted HRV, and often under-estimated at the design stage, not so with the Breathing Window. With subtle architrave ventilation detailing, threshold gaps and some ventilation of bedrooms to cross-ventilation zones, we ensure gas equalization throughout the building, with typically 2 units acting as the lungs of the house. One unit running at medium speed (100m3/hr) provides enough fresh air for 4 people (Passive House requirement are 25m3/person.hour).

Up to 15 times better heat transfer efficiency at the heat exchanger when compared to standard flat plate heat exchangers gives the breathing window higher system efficiencies.

In delivered volume comparisons, the breather window has 60% less pressure drop in the system caused by ductwork used by other units. This results in lower fan speeds, greater efficiency and greater savings for you.

Due to the small dimension of our heat exchanger, most moisture leaves the building as saturated vapour, which means less frost occurrence and less defrost cycling compared to standard units of similar efficiency. A FiWi unit tested in Iceland had a 95% lower defrost cycle rate than standard HRV units.

Standard HRV systems suffer from high thermal resistance at the exchanger surface due to the boundary air layer. As heat is exchanged by the copper wire in our FiWi exchanger, the boundary layer has little or no effect on heat exchange, increasing efficiency. Our competitors often rely on heat loss from inefficient fans to boost their efficiency figures. Our high-quality fans lose very little heat, and yet we have still measured 85% heat-exchange efficiency in an installed unit. At -10 degrees outside, a breathing window has been measured supplying fresh air of 17.5 degrees to a building at 20 degrees. Most of our competitors only achieve such results in the laboratory! We can increase this to 92% by weaving the wires closer together but the pressure drop through the heat exchanger increases canceling the gains.

So, this is the direction I am going in...

Best,

-AC