I have performed basic testing using a freezer to determine sensible efficiency, because winter has not come yet.

Latent efficiency has also been measured with and without desiccant, briefly. Latent efficiency changes with conditions, the colder it is outside, the higher the efficiency.

Testing was done with approximately 0 degrees and >90% RH " outdoors", 21 degrees and 50% RH indoors.

The sound level measurements are from the spec sheet of the fans.

Electrical consumption is measured using a VOMM and should be within a few percent.

The openERV will include systems that prevent unbalanced flow due to wind, which greatly reduces real world efficiency for the other units on the market, but is not reflected in their quoted figures. The standard testing protocols, scandalously, do not factor in any imbalances in pressure due to wind or other factors.

This data is for the 4.0 beta model, changes will improve flow rate but probably not change efficiency much, because it will use the same thermal wheel. Version 5.4.2 gets 27 CFM on max.

The table below doesn't work on mobile. Basically it says 22 CFM max flow rate, 88% efficiency, 37dBa, but 10 CFM 91%efficiency and only 22 dBa (0.3 sone) at low flow setting. You can adjust it anywhere in between there.

88% efficiency means 88% of the heat from the outgoing air is returned back into the dwelling.

For exactly how many kilowatt-hours, joules, and cubic meters of natural gas and carbon dioxide you save, see the spreadsheet on the Why OpenERV? Page.


OpenERV V4.0 Beta Performance Specs

This is the spreadsheet I used to get an idea of the impact that wind can have in the absence of fan speed automatic compensation. It's kind of complicated to explain. There is the fan static pressure, which means the pressure the fan can exert when airflow is totally blocked, the pressure that it can exert at the specified flow level that is the goal of the system, and the no load flow rate. It calculates the flow rate that would result from a certain wind pressure combined with the fan pressures as they change with flow, calculated from wind velocity and direction and typical fan characteristics (the curves are basically all the same general shape), and then calculates the amount of excess, unbalanced, flow, then calculates the net overall efficiency.

The assumption is that the compensated type of system suffers basically no changes to relative flow beyond the limits of the fans to compensate (which can still happen in high winds). The OpenERV will monitor the efficiency of the system directly using temperature sensors and compensate fan speed to correct deviations from optimal.

Desiccant only improved latent efficiency from 40% to 50% under test conditions, it would be expected to work better with higher water contents and lower temperature differentials, but isn't really worth the work and cost unless you DIY. It's easy to do, you just put some stuff from silica gel desiccant packets through a coffee grinder, then put the regenerator in a plastic bag with the powder and shake to coat the regenerator. Then wipe/blow/knock off the excess and put it back in. Eventually the regenerator will probably get dirty and need to be cleaned, which will remove the desiccant, so you would have to re-add it then.

Test data sheet, some of the specs above use inference between the test points.