TRACE 700 Results

[richiep]

All,

I have 2 questions in regards to my TRACE 700 output (FYI, I'm running the latest version - v6.2.6). I've tried contacting CDS Technical Support, but they can't seem to give me a straight answer to my questions, so I figured I'd give this forum a shot...

1) One of my AHU systems is running off of 100% OA. Therefore, latent cooling is being done at the main AHU cooling coil to partially dehumidify the OA. However, when I review the System Psychrometric State Points Report, the SHR is listed as 1.00. Not quite sure how that can be when there's obviously latent cooling being performed.

2) When I review the Design Cooling Coil Capacities Report, the Peak Plant Total Load is 365.1 TONS. The system peaks in July at 1500 hours. On the other hand, the Block Plant Total Load is 246.6 TONS. It claims that the block plant load peaks in July at 1600 hours. Any ideas as to why there is such a large discrepancy between the two values? I know the computation methodologies are different, however, I don't believe that justifies a difference of 120 TONS occuring an hour later.

Any light anyone could shed on these issues would be greatly appreciated as I am running out of options here.

 

[RossABQ]

I can't open TRACE at the moment, but check the definitions of Block and Total loads in TRACE Help. I believe one is simply the sum of peak loads in each zone; the other is the actual peak concurrent load. I would assume the Block load is the actual concurrent peak load, with some areas of the building (on the east and north sides) no longer at their peak.

Can't help with your first question.

 

[richiep]

Hey RossABO,

Thanks for the advice. I knew the differences of each simulation run type prior to running the model; however, I didn't expect the difference in totals to be so great. When I spoke to CDS Technical Support even they had agreed. I sent over the file for them to review. They said they were able to get the block plant total load to around 340 TONS (as opposed to my 246.6 TONS). I wasn't able to mimic their results. I don't know what I'm doing wrong.

 

[NCDesign]

I just double checked a Design Cooling Capacities report from a project I previously ran in Trace and it does not list a time for the Peak Plant Loads only for the Block Plant Loads. The only obvious error from your description is that Trace has assigned a time to your peak load. By its definition a peak load does not have a specific time associated with it. Also keep in mind that the delta between your peak load and your block load is very dependent on your floor plate, building orientation, usage, etc. A single story building with a lot of wings that have different orientations, a lot of variation in glass %, and not much 'interior' space could give you a very healthy difference between block and peak loads.
Also, keep in mind that interior load schedules matter when calculating loads in Trace. If you are doing load calcs and don't use the "Cooling Only (Design)" schedule an interior space may peak at 10:00 a.m. because Trace figures 100% occupancy at that time due to your schedule and then when it is recalculated at the block load time (3:00 p.m. in your example) the people schedule may have the space only half full. A conference room with a full load occupancy of 30 people would have a drastically different load under those two conditions especially when outside air is included.

Your first issue is not easily addressed without seeing inputs and outputs. It is very easy to think you have everything entered correctly in Trace and get a screwy result only to find that the real error is with the inputs. I have learned way to much about Trace via this method.

 

[richiep]

NCDesign,

If I'm not mistaken, the Peak Plant Load is equal to the total capacity of the cooling coil selection section found in the System Checksums Report. Within that report, it states that my design peaks in July at 1500 hours.

I thank you for your response. I'll have to investigate this further. Unfortunately, there isn't an easy way.

 

[cry22]

What do your engineering checks say for your block load? do they give you a SF/TON that you'd expect or not?
If your block load is say 700 or 800 SF/TON, then Trace folks are correct in giving you 340 SF/TON.
if you have a total enthalpy wheel for heat recovery, you should be around 500SF/Ton in your block load for a standard office building in the mid-atlantic US.

Of course, it depends on your local climate, % glass, low-e glass or not, is heat recovery applied? DCV, etc.

Please issues these kind of data along with engineering checks from your output for people to make a better judgment.