Rule-of-Thumb - How much heat-gain can be dealt with using Natural Ventilation

energymodelling
#1

Hi There

I came across this useful graph in an ASHRAE article a while back (do not have source unfortunately - please add if you know it).

ACH vs Cooling Capacity (Nat Vent).JPG811x517 40.4 KB

I have found it quite useful when using with energy modelling work in residential applications. I.e. check the loads in a space in W/m2, then get a gut-feel of the air changes needed to dissipate these loads and whether it is in the realm of natural ventilation for the space.

I would be interested to get others’ thoughts on whether the chart matches their experiences though.

-Francois

#2

Hi Francois,

The graph above comes from one of the papers published during the preparation of the book “What Colour is Your Building”.

The paper is one of many written while researching the book but do not form part of the book nor has been peer reviewed. They merely support the statements made in the book. All the papers are free to download should you be interested.

My advice would be to read the paper and see if the graph supports the applications which you are using the results for.

Link to the book:

Link to the paper:
http://www.cundall.com/Cundall/fckeditor/editor/images/UserFilesUpload/file/WCIYB/IP-20%20-%20Ventilation%20rates%20in%20offices%20-%20mechanical%20and%20natural.pdf

Link to the library of papers for the book
http://www.cundall.com/Knowledgehub/knowledge-hub-search.aspx?categoryid=66

Yogesh

#3

Hi Francois,

You can relatively easily draw this graph by yourself by performing an energy balance using Q=m.Cp.dT. Then you would know where the data comes from and can compare it to this source.

I would recommend using conservative temperature difference for design purposes, because normally sensible cooling is the highest when outdoor temperature is the highest (i.e. lowest temperature difference).

Best
Thomas