Evaporative Cooling System

Akshay Pahade
LEED Consultant
May 15, 2014

Optimize Energy Performance

We're working on a factory + office building, of which only the office area (10%) is conditioned using VRF systems and the factory area (90%) is being cooled by using evaporative cooling system.

Which of the following approaches for energy simulation is acceptable? If not, why?

Case 1: (Only office conditioned)

Baseline System: Packaged single zone heat pumps (System 3)

Proposed System: VRF for office areas,

evaporative coolers modeled as ventilation fan load for Factory areas (same in baseline & proposed)

Case 2: (consdering entire area conditioned)

Baseline system: VAV with PFP boxes (System 8)

Proposed system: VRF for office areas

Evaporative coolers with [thermostat + humidity control] for factory area

Need recommendations!

Thanks in advance :)

Answer:

Author

Divya Nambiar

May 17

1 users voted0 users voted

Answer:

Using an evaporative cooling system, at a location where, the ambient weather conditions allow the same, is an effective way to reduce energy consumption and so, a sustainable strategy. I suggest Case 2 as a more relevant modeling option. 90% of the floor area is factory space and as per ASHRAE 90.1, - an enclosed space within a building that is cooled by a cooling system whose sensible output capacity exceeds 5 Btu/h·ft2 of floor area is a conditioned cool space. For the proposed case, modeling the entire space (office + factory serviced by evaporative cooling) as a conditioned space would make more sense. Also, using a evaporative cooling system is a more cost-effective strategy. To show the actual energy efficiency of the units, annual average, peak conditions, volume of air delivered in various modes and water usage should also be factored. Another major consideration, is the type of evaporative cooling system that you are using - direct, indirect or hybrid. A DEC (direct evaporative cooling) system can affect indoor comfort issues due to high humidity. Also, it would be a suggested option, only if, the factory product is not affected by moisture. e.g. paper and fabric factories do not prefer DEC as the right alternative. Overall, it would be a preferred option in dry climates. These are usually used where industrial spot cooling is required and the function does not affect occupant comfort.

The mineral content of the water must also considered when using an evaporative cooling system. In places where water has a high mineral content, and if the same water is circulated over and over again in the system, over a long time period, mineral scales and deposits may be accumulated over the evaporative medium.

I have heard of issues in modeling VAV system with PFP boxes in certain softwares like design builder and eQuest. Energy Plus is said to be more effective in modeling the same. So, you can ask your energy modeler to try this out first. DOE2.1E simulation tool would is also effective in modeling these baseline parameters.