Passive heat recovery ventilation and cooling bug?

Bobby Gilbert · Posts: 20

I have tried to put together a system that mimics the wind driven passive heat recovery ventilation system used on Zedfactory projects such as BedZed in south london.

I have tried to model it as a mechanical HRV system with 100% efficient fans, with no aux load, and no transfer heat to the input stream. My setup is shown in the screenshot below along with winter design week output.

2 questions:
- Does this look right? (see attached hvac spec) The system does not actually use fans at all, it has a windcowl and relies on a compbination of wind pressure and stack effect to drive it. It has a 70% efficien heat exchanger and works at between 0.25 and 0.7 ac/h depending on wind speed. I've simplified this to 0.4 ac/h with 70% heat recovery as a constant.
- Why do I get a cooling load? I have cooling turned off at the top level and have checked that it is not on at any level below that. Have I misunderstood one of the parameters, e.g. heating setpoint temperature? I'm running with compact HVAC and with calculated airflow with natural ventilation as well (windows are open in summer).

Full file available if this helps.

Andy Tindale · Posts: 1197 Location: Stroud

The set up looks about right though it would be more revealing to see the model data on the HVAC tab.

The cooling load is probably the cold air coming in through the HVAC system supply. See definition for Zone/Sys Sensible Cooling in the program help.

Andy

Bobby Gilbert · Posts: 20

Thanks Andy. This now makes sense.

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