Current Energy Codes and Office Renovations

 In my research paper, ASHRAE 90.1-2010 and IECC 2012 were compared in the context of Chicago urban tenant fit-outs.  IECC 2012 was concluded to be the better option under the specific case study of a downtown Chicago office building with a 30,000 SF floor plate, steel frame, and infill window wall with 47% glazing.  Envelope, Electrical, and Mechanical sections of each code were compared to see what the baseline codes call for to reduce the waste in Office building energy usage.

 

 

In terms of the envelope, the area was fixed (8,030 SF) and the design temperature differences were also fixed (summer=18F and winter=82F).  This left the U-value as a variable for the heat flow equation.  ASHRAE calls for 0.45 U and IECC calls for 0.38 U for glazing, which is the dominant envelope material for Offices.  This seemingly small change decrease in ASHRAE’s resistance leads to 4.8% more gains in the summer and 15.5% more losses in the winter.  Looking beyond glass at the total UA value, we get 1,434 btu/hrF (IECC) and 1,698 btu/hrF (ASHRAE).  Simply due to window U-value the ASHRAE assembly allows 13% more flow.  Lastly, in terms of infiltration, ASHARE allow more flow through the windows which brings in pollutants or unwanted air directly into the occupant’s breathing zone.

 

 

For Mechanical systems, we can estimate total loads for an office.  The total heat losses in the winter come to an average of 145,000 btu/hr between the codes.  Relatively speaking, the internal heat gains are greater than this when considering the people, lighting, and equipment gains of 186,000 btu/hr.  This leads to a net heat gain so the systems are cooling throughout the year.  For equipment efficiency, a packaged terminal air conditioner should have a 15.9 EER (IECC) and 19 EER (ASHRAE).  Here, ASHRAE will save 25% more energy on cooling the spaces.  For demand control ventilation, IECC call for the system when 25people per 1,000 SF are present.  This will create a more efficient space such as a conference room so that ventilation is only brought on if needed.  ASHRAE only calls for this control when 40people per 1,000 SF exist.

 

In terms of electrical controls, ASHRAE calls for 50% of the power receptacles to be switched off automatically either when not in use or after-hours.  Typically, in an office building the computers are the main energy user and they are plugged into the critical receptacles which stay on 24/7 to avoid data loss.  Due to this, the power auto-off requirement will not save much more energy than typical.  Monitors, appliances, and some others may be turned off after-hours.  As for lighting controls, IECC has slightly better lighting power density (LPD) numbers.  LIghting is the number one user of energy in office buildings.  They are densely spaced and on very often.  Both codes maximize the use of daylighting through various controls.

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