Good Afternoon Everyone,

I am modeling a building which has unconditioned stairwells with emergency
water piping running vertically to the top. During the renovation there was
concern that during the winter months those pipes could freeze. To prevent
that the HVAC engineer added unit heaters on the first floor of the
stairwell to maintain the temperature no less than 40F. I think I input
everything correctly to my model to account for this load but the results
are not what I expect. Here's what I did.

I created a new thermostat schedule for heating at 40F year round. I then
changed the system type to a unit heater. Under the system heating tab I
specified it was electric heat and entered the heating capacity. Back in
the zone tab I space type from unconditioned to conditioned and specified
the new thermostat schedule. Since there will be no cooling I specified a
very high design temperature (100F) so that I would not have any unmet
cooling hours. Under the zone heating tab I then specified a maximum
heating rate.

When I ran the model I saw very little overall consumption change(which I
would expect), however, the heating load went down slightly, the cooling
load went up slightly, and the fan load increased the most. Is this not the
right approach for adding this kind of load the building? Has anyone ever
added something similar? Thanks for any advice you might have.

Michael Shields