I have 222 thermal zones. This is a standard size project. I am trying to increase the turn around time on my current simulation.
For the proposed design model:
I have modelled each of the 13 AHU including the VAV air terminals to all zones. In the proposed design there exists zone equipment including radiators, floor heating, chilled ceiling, fancoils.
For each zone, I propose to sum the equipment capacities of all zone equipments to create a single ideal heating/cooling "machine" to be found in that zone. The rated electrical consumption of all motors for the fancoils will be sepperately summed and entered as a user which does not impact on zone thermal loads (process equipment). A PLE (0.5) for the fancoil fan power will be assumed and held constant for when the "machine" is on, and this will be devided by the rated electrical consumption of all motors for the fancoils.
The CW and HW energy used by this zone "machine" will be converted into kgPh HW or CW mass flow to account for pumping power based on a dT of 20degC which is assumed an average for the zone equipment (eg. for heating radiator --> 20, fancoil --> 40, heated floor --> 20, ect.) This means the mass flow demand to the Chilled and Hot Water Plants will be inaccurate, but the energy delivered will be 100% accurate. In inaccuracy will result purely from an inaccuracy in resulting pumping power. This is only for the zone equipment. The main AHU and VAVreheat if there is any is 100% accurate.
ASHRAE 90.1 does not really elaborate on the modelling of the zone equipment. The baseline does not have any.
Would this fall into a "exceptional calculation method"?
Would you invest a 6 month period just to model all the zone equipment in detail?
Regards,
Jean
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
September 26, 2012 - 2:01 pm
Use the ECM if claiming savings for a non-regulated component (i.e. elevators), if you need to violate a modeling protocol to show savings (i.e. vary a schedule) or if using a work around in the model because your software cannot model something directly (i.e. daylighting in HAP). This certainly sounds like some kind of work around to me.
Hard to say how you would model something like this as it is usually very software dependent. If a model takes 6 months then it would be one of the most complicated models I have seen and I for one could certainly not afford to spend that kind of time.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
September 27, 2012 - 4:17 am
Thanks Marcus,
I usually model with eplus. This time I'm using TrnSys. These are both very powerful engines and can model, just about anything.
I guess my point is that one can model practically everything down to the pressure drop in the hydrolic system...but it takes too much time. If there where just a few zones with not so much variation in zone equipment, then I would do it.
This is a work around, due to practical modelling needs. So I guess that qualifies as you said to use a ECM for that part of the modelling. As far as practically possible we model the proposed system as designed.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
September 28, 2012 - 3:02 pm
EnergyPlus and TrnSys can model just about anything and take considerably more time to do so in my experience. Now I understand the 6 month comment.
You are really touching on the art of energy modeling. How can you simplify the model without compromising accuracy to a significant degree? In my experience there is a rather large grey area on this issue, not a thin line, and it varies on practically each model.
Santiago Rodriguez
Revitaliza Consultores65 thumbs up
October 15, 2012 - 2:09 pm
I was looking for older posts regarding thermal zoning, and this is the closest I found relative to my question.
Ashrae 90.1 2007 describes how you should model the thermal zones of your building, and it basically says you should define them as they are in the HVAC drawings, with some exceptions. I usually never model all physical zones, but rather group them together based on the orientation, type of activity and the HVAC unit that serves them. My questions is how far can we group zones in order to simplify the model?
In my case I am modeling a laboratory building and it has many internal zones which I want to group in only 4 groups, depending on the orientation. Otherwise the model will get too big and complicated.
I have seen studies where they compare simulation results of a building modeled exactly as it is and modeled with less zones and the results do not differ more than 1%. Of course it is very dependent on the type of project, but I think that thermal zone grouping is very helpful to minimize simulation time.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
October 15, 2012 - 2:38 pm
See Table G3.1-7 for guidance on modeling thermal zones as you describe.