# Calculating heat recovery from ventilation, how can i solve this?

I have a ventilation system with rotating heat recovery in my house.

It can recover about 70-80% of the energy in the air that is ventilated.

I would like to monitor what is happening. So i installed 4pcs of DS18B20 in the system.

I also installed on CT on the powerchord for the ventilator system, and the AC-AC adapter to monitor voltage.

I also have pulsecounter on the main utility meter.

-Incoming air temp C from outside (T1)
-Air temp C going into house after recovery (T2)
-Air temp C going out before recovery (T3)
-Air temp Cgoing out the chimeny (T4)

So, by taking the difference between (T3-T4) and (T3-T1) , and then dividing them (T3-T4) / (T3-T1) i can get the % of recovery in degress (not energy because of humidity beeing different).

I tried so many times to set up this in the EMON CMS but i cant get it to work.

How would i do this?

Very thankful for your input guys!

I am using the EmonPi with the SD card that came with it from the shop. System version 8.5, seems somewhat stripped from what i am used to on the emoncms.org website.

I also have problems getting the pulsecounter from my utilitymeter to show a normal POWER feed and a ENERGY feed.

//GF

If I understand the problem, its that the input process list is processed in sequential order with no way to control the hierarchy of operations. So you can’t compute the inside/outside differential before dividing.

Although I’ve never used them, it appears you can use feeds in an input process list. So you might try creating a feed that is the inside/outside delta T (T3-T1), and then in the input process list for T3-T4, multiply by 100 then divide by the inside/outside delta T.

There is a snag in that both of these calculations start with T3, and so would normally be in the T3 input process list, but you can only do one from T3. So to get around that, you might try subtracting T3 from T1 in the T1 process list, then doing a signed to unsigned to make it positive. (if you need this to work in cooling mode as well as heating mode, then remember to do signed to unsigned in the T3-T4 calculation.

Don’t know if all this works on the Pi. I only use eMnCMS. Hope this helps.

BTW/ in addition to humidity, a difference in volume in the supply and exhaust streams will reduce accuracy.