AC hard sized, number of people and variation of the inside temperature

asked 2018-11-26 01:59:54 -0500

Alexis gravatar image

updated 2019-01-03 00:24:57 -0500

I did a auto size simulation in the purpose to find the cooling capacity of every rooms as a reference for my HVAC equipment selection. After that, I asked the supplier to give me the equipment type that match with my cooling capacity calculation result.
So I hard sized the "cooling gross total rated total capacity", "the cooling supply air flow rate" and the pressure according to the supplier's reference. Until here, no issue.
Then I want to know how good the AC equipment would be in withstanding larger number of people inside the room, compared to my design condition, by looking at the impact on my zone temperature.

I am not sure of my reasoning but I have noticed something :
- I checked and compared the "Zone sensible cooling" table, column "Calculated Design Load" with the "coil sizing summary" table, column "Coil Final Gross Sensible Capacity",
- When the "Calculated Design Load" exceeds the "Coil Final Gross Sensible Capacity", the inside temperature increase,
- When its the contrary, the temperature is equal to my set point.

I post this question because I did some tests and I am surprised with the results. My room is sized for 35 people and when I set 200 people, my temperature increases by barely 1deg C. So I am not so sure of my reasoning above.
Would it be possible for you to check whether I made good method or not, based on my objective here?

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When you performed this test (switching occupancy from 35 to 200 people), did you do this for an entire annual simulation or just for a day or hour? If so, what day/hour? Additionally, can you specify the type of system you are working with?

The results are surprising (assuming your original room size/occupant density isn't something outlandish). My initial instinct is that this has to do with either building mass or a sizing factor that may have been applied by the manufacturer, but I would need more information on your process.

jmbattis gravatar imagejmbattis ( 2018-11-28 10:56:11 -0500 )edit

I did this test for the sizing day to easily compare the results. I work with a VRF system and a DOAS with HX for the fresh air.
I have two leads which can explain this results :
- my room has a huge volume (7m under ceiling), so to increase the temperature, I need more load than a classic room (3m under ceiling)
- according to E+, my room has a cooling capacity of 24kW but my supplier give me 28kW,

In fact I am not really sure of my reasoning, I mean, check "Calculated Design Load" and compare to "Coil Final Gross Sensible Capacity", to explain the increase of Temp

Alexis gravatar imageAlexis ( 2018-11-28 19:53:33 -0500 )edit