Trane Trace Design Airflow
Trane Trace Design Airflow
(OP)
Hello,
I'm a beginner in Trane Trace 700, and I'm having a problem I can't figure out. I'm doing load calculations for a building. I ran the calcs and everything came out OK. The procedure for me now is to go through the OA calculations using ASHARE 62.1 excel sheet (the company advises us not to use Trace ventilation method). Now that I hve the new OA numbers, I'd like to add them to the rooms, but I also want to specifiy the design airflow for the room so I don't have to go through a new set of OA calcs when Trace outputs a new design CFM.
I attempted to set the "Main Supply" airflow in the airflow tab for the rooms, but the airflow was still off by around 10%. I can't figure out why, but the design/space CFM is not coming out to what I specified. Does anyone know what the problem might be?
I'm a beginner in Trane Trace 700, and I'm having a problem I can't figure out. I'm doing load calculations for a building. I ran the calcs and everything came out OK. The procedure for me now is to go through the OA calculations using ASHARE 62.1 excel sheet (the company advises us not to use Trace ventilation method). Now that I hve the new OA numbers, I'd like to add them to the rooms, but I also want to specifiy the design airflow for the room so I don't have to go through a new set of OA calcs when Trace outputs a new design CFM.
I attempted to set the "Main Supply" airflow in the airflow tab for the rooms, but the airflow was still off by around 10%. I can't figure out why, but the design/space CFM is not coming out to what I specified. Does anyone know what the problem might be?





RE: Trane Trace Design Airflow
You should call Trane support ( it is free with your nandatory subscription).
RE: Trane Trace Design Airflow
i don't use trace, but common fault in such setups is when concepts of supply air and outside air are mixed. most of load calcs software provides supply air calculation, and fresh air setup stands somewhere besides that.
RE: Trane Trace Design Airflow
To specifiy the desired design SA CFM, the block cooling airflow must not be filled out for the system. That's the only way to specify the SA CFM. Of course, that means that for a single system, you'd need to specify all of the zone SA CFM's so that you get to your block cooling airflow (from the AHU).
RE: Trane Trace Design Airflow
leave it blank and it will give you a different CFM
BUT, watch out if you get a too high SA temperature, you'll end with dehumidification problems.
suggest that you give your file a generic name and post a TAF file for others to see.
You know how to make a TAF file, don't you?
If not, close the file, go to file/archive project, click on the TRC file and an archived TAF file will be generated, post that file and we can check it out for you.
RE: Trane Trace Design Airflow
For the outside air calculations, we design based on the peak design CFM for the VAV (in our case VAV with hot water RH). I got the OA numbers I needed to satisfy ASHRAE 62.1, and I inputted that into Trace as a CFM value. I set the SA CFM to the peak design of the VAV box.
However, I'm designing the system based on the Block CFM, not the peak. Regardless of which CFM I'm designing to, the CFM/ton comes out to around 220 which isn't easy to get fromn an off-the-shelf AHU. When I got selections, the CFM for the AHU was 65% over the design CFM specified by Trace, in order to meet the cooling load requirements.
What would be the procedure now? Should I bump up all of the VAV CFM's in order to get a total CFM that matches the AHU, re-do the OA calculations, and re-input the values in Trace? Or is there a standard method for adjusting the OA and load calculations based on the selected AHU? As Cry22 mentioned, the SA temp should change since the cooling load is relatively the same, but the CFM is a lot higher. However, the numbers in Trace stil have the specified SA temperatures, so I'm having trouble figuring this out.
Any help would be greatly appreciated.
RE: Trane Trace Design Airflow
RE: Trane Trace Design Airflow
RE: Trane Trace Design Airflow
RE: Trane Trace Design Airflow
can we go step by step, for instance if you would reveal how trace's supply air calculations are tied to your change of oa settings, we could possibly go forward...
RE: Trane Trace Design Airflow
This is easier to understand, less error-prone. Also easeir to show to AHJ what you did.
I once did a full ASHRAE calcaultion in Excel and Trace and never really had 100% the same numbers, they always were a bit different whne you include all the ASHRAE loopholes. And this didn't even work well with exhaust.
Here in WI code for ventialtion is different from IMC/ASHRAE. So what i do is calculate OA for code, OA for ASHRAE and pick the higher number. In addition we have often huge exhaust requirements, that supersede the OA requirements. In tha tcase the OA is overdesigned anyway. This is not easily doen in Trane, if possible at all.
Trane is really really good. but if you don't understand something 100% you easily do it wrong and get totally wrong numbers.
RE: Trane Trace Design Airflow
I have the required OA calcs from an Excel sheet. I inputted those values in Trace and I'm getting the cirrect OA outputs. Now, I took the block capcacity, the SA CFM, and got selections for an AHU. The CFM/ton based on the Trace file was around 220, which is too low to get a good match from an off-the-shelf AHU.
The selection I got from the sales rep had a 65% higher SA CFM than the one Trace said I should have. The question is, what now?
PS. HerrKaLeun, yea Trace is funny like that. We're actually supposed to do energy modeling with Trace in a later phase of the project. I've never done it before and wonder how accurate the results will be. I heard somewhere around +/- 20%!
RE: Trane Trace Design Airflow
i have to guess and say that block load and ventilation load are summed up to reach reference data for your ahu?
on the other hand, i also have to guess that you have no any other choice but to take some packaged rooftop with fixed ton/cfm capacity.
first you should do is to check whether calculated minimum cfm can be reached by controls with your picked ahu at all. if not, you simply have to change ahu selection concept, give up locking supply temperature or similar. changing supply air temperature should reduce collision.
it is also interesting to see how much block load differs from peak loads sum? if you are limited with ahu choices, there could be, for instance, possibility to split into two completely separate systems where two separate ahu's could fit.
no tool i use is a magic tool. best of them have most of useful options, but we always have to be aware that each of them have their own limitations.
RE: Trane Trace Design Airflow
If you use Trace for load anyway, it is natural to use it for energy simulation. But you should know what you are doing.
RE: Trane Trace Design Airflow
HerrKaLeun: Oh yea, I can't wait til I have to re-do the energy model 10 times to figure out what I inputted wrong haha.
RE: Trane Trace Design Airflow
You also can insert the actual equipment unload and ambient relief curves etc.
Many energy simulations are not detailed with HVAC options. So the user can't do much wrong.
If you enter everything right, Trace will be accurate.
One issue with all energy simulations: they simulate the assumed occupancy and usage and also assume the system was properly commissioned and works as designed. In reality this isn't the case.
RE: Trane Trace Design Airflow
RE: Trane Trace Design Airflow
the energy simulation, in my opinion, is to decide on what system is to be chosen. the owner can use upfront cost, maintainability, energy consumption etc. to make a decision. it isn't to predict exact consumption.
just for the fact that the energy simulation uses TMY3 or some other weather data (which are an average design year) will make it impossible to compare one year to the simulation.
RE: Trane Trace Design Airflow
I'm hoping one day we can get a project where the client cares more about efficiency and long-term returns than initial cost and deadlines.
RE: Trane Trace Design Airflow
Just an idea...