[Equest-users] General Questions:

Kelsey VanTassel KVanTassel at sustaineng.com
Thu May 20 12:29:29 PDT 2010


I can tell you some of the assumptions I routinely make for energy models, but what you should use always depends on what the goals for the energy model are.

Kelsey Van Tassel
Mechanical Engineer | kvantassel at sustaineng.com
Sustainable Engineering Group
901 Deming Way, Ste. 201
Madison, WI 53717
608.836.4488 ext. 20| Fax: 608.836.4477

General questions:

1.  I went room by room and input actual equipment.  Example: I have 1
computer per person in a workstation.  155 Watts/computer from ASHRAE.
(Includes CPU and monitor)

1-A.  Is this a constant 155Watts.  Would the load be constant for printers,
projectors, refrigerators, dishwashers, microwave ovens, server rooms,
elevators?

No, the loads are probably not constant. The easiest thing to do would be to make a reasonable estimate for how much power is consumed when some or most of the equipment is on (it is unlikely that every single piece of equipment would be on at full power all at once, though). Input that power density into eQUEST and make sure that the hour-by-hour profile (consisting of fractions of that peak load) is reasonable based on your occupancy schedule.

2-B.  I was given the server heat or rejection.  Does the server really put
out that much at night also?

Maybe. Were you given a maximum or an average? Did you set up a separate schedule for the server load?
  
3-C.  I use ASHRAE recommended values, but I assume these are for loads, not
hour-by-hour year round modeling.  Are there other guides?

I use Table N2-3 from the California Nonresidential ACM Approval Manual which lists receptacle loads found from a study conducted by Lawrence Berkeley National Laboratory.

2.  I currently have my infiltration set to 0.3 ACH for my exterior rooms.  
2-A.	Are there accepted or standard values?

Section 27.23 in the 2005 ASHRAE Handbook of Fundamentals discusses Nonresidential Air Leakage. In it, they cite a 1976 study done on 8 Canadian Office buildings with sealed windows which showed an average air leakage rate between 0.12 and 0.48 cfm/sq ft wall area. I have been using 0.12 cfm/sq ft wall area for perimeter spaces for all of my models unless I am specifically studying infiltration reduction. This value is about 3 times higher than the eQUEST default.

I would be interested if anyone knows of any more recent or comprehensive studies.
 
2-B.	Should I use ACH or cfm/sq ft of wall

It doesn't matter. eQUEST treats both the same. There are other infiltration calculation methods available in detail mode, but they are mostly for residential buildings, I think.

2-C.  Does the baseline and purposed need to be the same?

It depends on what the energy model is intended to show. But in general, the weather file, occupancy schedules, building footprint and floor plans and process loads are kept the same.

2-D.  Is there a set standard for the baseline?

Depends on what type of energy modeling you are doing. If it is for LEED, you must follow ASHRAE Standard 90.1 Appendix G. State incentive programs, utility programs and energy tax credit rules will all have different requirements for the baseline model. If you are trying to show energy savings of upgrades to an existing building, your baseline will be the current as-built design.

3.  Thermostat.  
(Positive note!! Instead of thinking of changing "night-time set back" values
as gaming, I should look at it as finding the best way to operate the system.
I think I am starting to understand!!  If setting the thermostat back 10
degrees saves energy, I should do it! And the model shows me what to do!)

Sure, just be careful that the assumptions you are making are realistic.

3-A.  Besides the owner's request are there any rules for thermostats?

Just to be careful. You may be able to model controls that are not really realistic. Such as having a very narrow deadband (difference between setpoints for heating and cooling mode) or temperatures that are controlled very precisely to within 0.5 deg.

3-B.  Some have modeled heating only spaces as having a cooling system but
set the thermostat set point very high so it would not turn on.  Is this an
acceptable method?		(Example- I have a mechanical room which is
cooled by an exhaust fan when the temp is above 80 degrees, I modeled the
unit to turn on when the temp reached 95 degrees.  The result it the cooling
never turns on, since the exhaust fan offers enough cooling.)

That is one way to do it. In rooms where the temperature is allowed to float, I remove the heating and/or cooling t-stat schedules entirely. 


4.  Odd rooms.  It is easy to model office spaces, but I have found
electrical rooms, mechanical rooms, elevator equipment rooms, vestibules,
stairwells, and server rooms to be lacking on guidance.

4-A.  Is there any resources besides general judgment?

I generally find these types of rooms fairly easy to model since they usually do not contain people for any significant amount of time. Ventilation or exhaust is determined by square footage. The hardest part is determining an appropriate receptacle load.

5.  Minimal model.  There is a lot of information which can be input.
Besides general gut feeling, how percise should the model be?

This again depends on the goals for the energy model.

5-1.  If I leave all the thermostat "by zone", and don't actually model the
thermostat in the room is this okay?

It could be. Would all the rooms normally have individual thermostats? Are you grouping only similar rooms?

5-2.  In an office, how do I schedule the meeting rooms?  Do I show that the
population in the general office drops when everyone goes to the meeting?

Unless you have the building divided up into multiple shells, there is only one occupancy schedule that is the average for the entire building.

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