Hello,
I have a project that is classified as low-rise residential. It will use a 2-pipe fan coil system and will get its ventilation from operable windows. Does anyone have suggestions on how to model this? I tried to use the Natural ventilation tab but it does not activate for fan coil units and I do not know how to get natural ventilation and a chilled water system to work together.
I am assuming that when it comes to cooling and heating that I just put the OA requirement for the room in the system and it will be the same thing as getting it through the window. Correct? However I do not know how to account for someone opening the window to supplement the cooling and heating. Should I model an air-side economizer and just let that take care of any "free-cooling"? Does anyone have any suggestions or tips?
Thank you for any help.
John Grando LEED AP
John
The way you are describing the system, you might as well tack on your
ventilation to the infiltration values since essentially this is what
you are doing to the spaces.
Alan Jackson, LEED AP
John - If you do want to experiment with natural ventilation you will need to activate it in the Internal Loads tab for each affected space, under the infiltration sub-tab, not in the HVAC tab. I've had varying luck/results using the Sherman-Grimsrud method, and haven't tried out the ASHRAE method. I would suggest setting up some hourly reports based on the natural ventilation schedules you set up to make it work.
Good luck!
Matthew Higgins, Associate
LEED AP + ASHRAE-HBDP
You will have to provide some more detail on the controls of the
operable windows.
The problem I have with the economizer method is that if the windows are
manually controlled, you cannot capture the benefit from an energy
standpoint, you will need to provide some sort of smart controls to
handle the windows much like you would the damper for you traditional OA
system.
Alan Jackson, LEED AP
The windows are manual, but out of curiosity and a possible suggestion to the building owner, how would I get the Fan coil system to work with the operable windows if they were connected. Say, for example, whenever the window opens, a circuit is broken and it shuts off the fan coil unit. All of the natural ventilation options are grayed out on the HVAC system tab.
John Grando LEED AP
If the windows are manually controlled, I think a reasonable way to
model it would be as Alan suggested, as added infiltration, with a
schedule that mirrors the occupancy schedule, so the added infiltration
only occurs when the room is occupied. This way you are modeling your
minimum required ventilation but no more.
William Bishop, EIT, LEED(r) AP
Hello All,
I am trying to use natural ventilation in conjunction with a two pipe fan coil system for a residential building. I set the ventilation temperature schedule to 70 degrees, and the usage schedule to always on (all hours = 1). However I still have some hours where it is not turning on. I checked one hour when I had an unmet load hour and the outdoor dry bulb was 63 degrees. Does anyone know why the natural ventilation would not turn on. It is obviously cold enough to do some cooling of the space. Please see attached excel file.
John Grando LEED AP