Tuesday, September 25, 2012

The Energy Code Challenge

ASHRAE Standard 90.1 2010 will be “strongly suggested” to be adopted in codes next year. (October 18 2013 is the date mandated by the US D.O.E.) ASHRAE 189 2010 will push the envelope further, and will be code in a few locations. This revision to the 90.1 Standard, as well as the new 189 Standard, will impact the way we design systems. Just recently, I attended a seminar outlining the impact of the updated standards. 52 of the 110 changes to the 2010 revision affect HVAC systems. 25K sq ft, single zone, 2 floors or less, and constant volume is a lower limit on simple systems. The Performance Rating Method, appendix G, is not mandatory, but is used for LEED comparison purposes. The Standard provides both a “Prescriptive” and a “Performance” path. This allows some flexibility in selecting the design. Air cooled equipment will be harder and harder to comply with the Standard. Water cooled equipment makes lots of alternate systems practical, including using water to move and remove heat.

Some of the issues, and how they may affect us in the air distribution wing of the HVAC industry, are as follows:

Rooftop units: Chilled Water with 5hp fans or DX > 9 tons must vary the airflow rate at low loads, which means a variable minimum outside air flow rate. Dynamic Ventilation rate control is also required.

Economizer: Previously, economizer was mandated only in milder climates, but now it has “Moved South”. Smaller rooftop units must have this capability. This will make rooftop units more complex (and expensive). It may push for VAV in many spaces that were constant volume in the past.

Reheat: Restrictions will cause engineers to rethink how they control humidity. I suspect fan powered terminal units will continue to replace single duct / reheat units as the rules tighten up.

Energy Recovery (Time for suppliers to dance a jig!): Energy recovery will become a major component of any outside air treatment system. I suspect DOAS (Dedicated Outdoor Air Systems) will get a huge boost with this.

Other requirements: Half the electrical outlets will be shut off during unoccupied periods. Roofs must reflect heat. Interior lights must be reduced. Most importantly, appendix G (which defines ‘baseline systems’) is being modified, which affects the push towards implementation of new systems.

Duct Leakage is emphasized as a major energy waster, and the new standard has very tough rules.

Finally, perimeter envelopes are highly regulated. This is especially good news as the perimeter is where most of a modern building’s energy is being consumed.

The result of all these changes will be to further reduce the energy use in the interior of buildings. This reinforces the idea that the ventilation rate requirement is the load in the interior. As perimeters get better, the ventilation rate will drive them as well. All HVAC system strategies, be they VRV, WSHP, UV, Fan Coil, DV or any other method, all require ventilation air, which is becoming the major component of the load calculations. We will come to realize that these ventilation systems need to be pressure independent as ventilation demands change within a space. In other words, VAV systems will continue to be a part of ANY HVAC system.

Authored by: Dan Int-Hout, Chief Engineer Krueger