[Equest-users] Stratified Thermal Zone - ASHRAE Baseline

[Daniel Kaler]

Dear All,

I am modeling a space that has a thermally stratified zone and essentially a separate system to handle each zone. The space is 24ft in height with (2) large heat producing pieces of equipment. I am making an educated assumption that 90% of the heat produced by this equipment will reach a height of 10ft, which I am calling the stratified zone. The remaining 10% will be will be accounted for in the occupied zone (<10ft).

The occupied zone will be conditioned by an air handling unit providing 10,000CFM of conditioned air with ducts dropping to 8' AFF.

The stratified zone has a system that will exhaust the heat produced to the ambient. There are (4) louvers sized for 4,000 CFM that are open to the space, installed at 14'. (2) exhaust fans, each at 8,000 CFM are installed on the roof being utilized to pull the outside air, from the louvers, into the space and out to the ambient. The heat from the stratified zone is exhausted during this process.

I am currently modeling the proposed design exactly as described above. The conditioned space (up until 10ft) is handled by the AHU and modeled as a conditioned zone with design parameters of (70F/75F heating/cooling respectively). The stratified space is modeled as conditioned (although technically not conditioned) with system type heating/ventilating. The design parameters on this space are (40F/135 heating/cooling respectively). The system is set up to provided 100%OA at all times and I used an input of 0 for heating capacity of the system. Does anyone have an alternate way to model a set-up like this?

There is no defined scenario such as this in ASHRAE. I need to take account of the electrical load of the fans for the exhaust air, but am not considering the space conditioned. For the baseline system, I was considering modeling the stratified space exactly as I did in the proposed, with a modification to the efficiency of the system. This way I can account for energy savings by our fan selection and use Table 6.5.3.1.1 for the fan energy consumption of the baseline model.

Any feedback/input is appreciated.

Thanks

Dan Kaler EIT
Energy Engineer

MEP Associates, LLC   engineers | consultants | commissioning
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