Measuring efficiency of home air ventilation/heat exchanger unit

[samppa]

My project is to measure the efficiency of the home air ventilation unit heat exchanger that heat intake fresh air with used air exhaust. With Arduino sensor I measure all 4 input and output temperatures of the unit. The formula for efficiency is calculated and reported as extra metric. Efficiency = (T_FRESH - T_OUTSIDE) / (T_INSIDE - T_OUTSIDE), where
T_OUTSIDE is the outside temperature input to the device
T_FRESH is the temperature of Fresh air produced to rooms
T_INSIDE is the inside temperature of house
T_EXIT is the exhaust dirty air that exits the house (after warming the fresh air)

There is no perfect match for reporting efficiency 0-100%. Of course there are other metrics that can be used to convey the message, but a generic "efficiency" would be a nice addition.

The project is still in its infancy although the sensor works well and is waiting to be installed (sensors to be drilled to the pipes)..

[NotYetRated]

I guess I am a little confused as to the device which you are actually measuring.

This is a heat exchanger which is taking "heat" in from an outside source, mixing it with "exhaust heat" and producing "heat" for some system?

Are you talking a furnace of some sort? Efficiency is typically measured in terms of raw energy output/raw energy input for such systems.

[samppa]

@NotYetRated
Here in Finland the outside air is cold most of the year and the heating is a major cost for living in a house.
So the heat from air exhausted from the house is used to heat the intake fresh air by the ventilation unit.

Also we have the Sauna at least once a week (that is a room that is heated with electricity to 80 degrees centigrade and there is a lot of humidity due water thrown on the sauna stove - and also showers.
My interest is to see how the efficiency of the ventilation unit reacts during sauna. Also I may add some valves to the air pipes so that during heating of the sauna the ventilation is closed automatically. Then I want to compare the results and calculate the impact to the heating costs.

[TommyE]

@samppa Nice project, I have a Flexit heat exchanger myself and I would like to do somenthing similar. Today I use four different temp meters connected to a Fibaro Z-wave unit and then to Vera.

Regards
Tommy

[NotYetRated]

@samppa

Ahh I see, interesting. Here in Ohio, USA, we do not explicitly exhaust or intake fresh air(at least in most homes). Our HVAC systems recirculate air inside the home, relying on natural losses/door openings etc to supply fresh air.

[samppa]

@TommyE
I got my node finally up and running. It measures the temperatures, calculates the efficiency and reports that as dimmer value to vera. The dimmer value as efficiency looks a bit odd in the UI5 but that was the closest metric there was available. I hope percentage metric is added in the future. I wish I knew how to do that myself (and had enough free time)..

[samppa]

I also got some DHT11 and DHT22 sensors for the bathroom and the idea is to control the ventilation booster automaticallu after shower to dry the bathroom. The logic has to take into account the outside humidity too since it is useless to ventilate if outside is raining and 99% humidity..

[samppa]

If I find some cheap motorized valves for the 160mm pipes I would like to shut down ventilation from the sauna area when it is heating up. But retrofitting those to existing pipes under the insulation in the attic is perhaps too difficult so this is just a dream for now..

[Heinz]

Hello, this week I started a similar project:
I made a mysensors device that communicates with my Vallox digit se via RS485 and sends the current temperatures and the fan speed to my home automation controller.
I like your idea of calculating the efficiency!

[samppa]

@Heinz said:

RS485

I have the same goal, but the Swgon Casa (aka ILTO in Finland) 440 Premium that I have does not have RS485 connector..
But it has some other pins for reading and controlling (DDC Control) as 0-10 VDC signals that map to e.g. temperatures 10-30 celcius. But I have not yet learned how to read that with Arduino.

[samppa]

One thing to bare in mind with this way o calculating the efficiency is the electrical heater inside the unit that heats the air during very cold days when the exhausted air is not enough to warm up the air,

So when the electrical heater is on, the efficiency is bodus and showing very high results and may go even over 100%.

[RJ_Make]

@samppa I'm probably miss-understanding you, but wouldn't the electric heater be 100% efficient? In other words, for every watt you consume you would be outputting in thermal energy? I realized in many area's** it's not the cheapest form of heat**, but I think it's 100% efficient?

[samppa]

@ServiceXp said:

@samppa I'm probably miss-understanding you, but wouldn't the electric heater be 100% efficient? In other words, for every watt you consume you would be outputting in thermal energy? I realized in many area's** it's not the cheapest form of heat**, but I think it's 100% efficient?

Yes, but in this case the definition of efficiency that is interesting to know is the heat exchange efficiency i.e. how much of the heat dissipated is preserved and transferred to the fresh air influx. The idea is to save energy and avoid heating with electricity. So the heat in hot air exhausted from the room is re-used to warm the cold outside air.