HVAC System Overview:
I’m just learning about HVAC systems, so for my ease of understanding and clarity of modeling, I stuck to an air-based heating and cooling system. Since my project is located at Jasper Ridge, I also figured that the heating and cooling loads wouldn’t be so high that a radiant heating system would be far superior — maybe I’m wrong! Here’s an overview of what the HVAC system ended up looking like:
3D:
I used the Revit duct sizing feature to design my duct cross sections but not their layout (I placed all the ducts manually). As anticipated, the duct size began gradually increasing as we went upstream, and I had to make allowances for higher airflow in order to keep the ducts at a reasonable size. I never exceeded the following guidelines for airflow volume (from CEE 256):
First floor plan:
‘Second floor’ plan:
I don’t actually have a second floor HVAC system since the majority of my building is a single floor spread over a wide area, but I created a ‘second floor plan’ because I have a portion of my HVAC system located at a higher ceiling height in one of the exhibit areas.
My administrative wing has lower ceilings than the rest of the building (9’) — exhibit spaces have ceilings at 10’ or higher minimum.
Generally, my exhibit spaces and more public areas are not completely thermally sealed off (with doors and walls and such) and so they are thermally connected if they are served by the same air handler. Smaller sealed spaces such as conference rooms, seminar rooms, offices, and play rooms have their own thermostat controls because of their differing heating and cooling needs — I’ve placed individual VAV boxes for each of these zones (example below):
I had some difficulty connecting the ducting system to the individual air handlers, so those were omitted from the model for now. I connected ducts in such a way that the overall building would require five air handlers; four are placed in mechanical rooms and one is on the roof. A rough sketch of their locations is below:
With the exception of two zones, all spaces are both heated and cooled. The southern entry is unconditioned, as it serves as a transition space/buffer between the outside and lobby, and the unloaded western corridor is naturally vented only, since it is architecturally designed to be a kind of in-between indoor and outdoor space. Conditioning a completely unloaded glass hallway is also very energy intensive and would honestly be a waste of heating and cooling energy.
HVAC System Analysis:
My space schedule is shown below:
As previously described, all spaces are conditioned with the exception of the aforementioned two. All supply air flows that were specified are met.
I had quite some difficulty running the HVAC systems analysis on my laptop (took over 14 hours), but thanks to Glenn, I was able to get some information out eventually. This is a summary of my cooling system summary:
And heating:
As shown above, it looks like much of the cooling demand is not from the outdoor air/envelope, but from the internal gains from people and equipment. This seems to make sense from a regional climate perspective — the cooling loads in the Bay shouldn’t be too high, and cooling from a massive amount of people in the exhibit in summer months would definitely be culpable for higher cooling demand. As for heating, there is a lot more heat escaping through the envelope.
I’m honestly having some trouble interpreting these results, but it looks like there may be some thermal storage in the slab (?) and direct solar heat gain (?) that might be mitigating some of the need for heating and cooling (?), although I’m still a bit baffled by all these numbers and their sign conventions.
Model Coordination Interior Views:
Admin hallway:
Office:
North exhibit (highest ceilings):
Seminar room:
South exhibit:
Challenges:
As mentioned, I did have some challenges connecting the air handlers to the entire ducting system — I placed all the ducts before considering how they would connect directly into the air handler (even though I routed all the ducts from the correct location). Ultimately I found that the properly sized air handler was able to fit in all their corresponding mechanical rooms (which means I made enough mechanical space!), which was a win, but routing the ducts in was quite difficult.
Frankly, I also wanted to incorporate more passive heating and cooling strategies than I ended up implementing and wished we had some more guidance on how our window and slab design, etc ultimately played into our heating and cooling. I think I was pretty caught up in learning how exactly to even design an HVAC system for the first time in my life that I stuck to the conventional, and possibly not the most efficient system. I would definitely be more experimental if I had more knowledge to begin with — or just the next time around.