DualTemp Contributes to PPL Plaza LEED-NC Green Building Certification

"ASHRAE Standard 62 and LEED requirements combined presented new design and configuration challenges... We do the Standard 62 CO2 calculations directly on the ASIC/2-7040 unitary controller, without needing a supervisory controller." - Peter Lewis, Dual Temp, Allentown, PA

The HVAC system comprised a York modular AHU, with VFD, and 11 VAV’s, three of which were dual duct. The second duct was for outside air from the buildings main ERU. All of the VAV’s were series fan-powered with electric reheat coils. Three of the zones also incorporate electric baseboard heaters, used on the auxiliary heat output. Wall mounted CO2 detectors were used, as well as a CO2 detector on the outside air duct for a reference. Three of the zones also were integrated into the occupancy sensors. The AHU featured top of the line Ebtron airflow stations in the outside air and supply air ducts. Cooling came from the chiller, which is central to the building. The AHU did not have any local heat. The entire system was designed with more stringent insulation specifications, as the designed discharge air temperature was 45°F. In actuality, this was too cold, and require too much reheating based on the how much air we had to deliver to meet the ventilation needs.

ASHRAE standard 62 was followed very closely on this project. The AHU controller is an ASI Controls ASIC/2-7040. The 7040 used the multi space equation to determine the actual volume of outside air that it needed for proper ventilation. The zones with a CO2 sensor had a base ventilation rate, and a maximum ventilation rate. These were set by the Engineer. We compare the outside CO2 level with the zone level. As the difference went from 0 to 450 ppm, the OA requirement was linearly reset fro the min to the max CFM requirement. The zones with occupancy sensors went directly from the min to the max as the occupancy sensor went active. The zones without either method had a fixed CFM requirement. The 7040 then followed the multi space equation provided by ASHRAE to determine the actual CFM of outdoor air needed. A PID control was used to track the position of the outdoor air damper to match this CFM. An economizer sequence was also used. The actual position of the outdoor air damper was then determined by the greater of two needs: the actual volume of air needed as measured by the airflow station, or the position needed to maintain the mixed air setpoint.

Standard 62 was simpler to apply than the LEED requirements, which were somewhat challenging to interpret and put into practice. In some cases we had to rely on common sense. For example, simply turning off the cooling or changing the setpoint in an unoccupied room is not a good solution when balancing the need for LEED credits versus occupant satisfaction. If the occupant returns to an unexpectedly warm office they are going to call facility management and complain that the system isn’t working.

It would have been great at the time to have other resources experienced in LEED processes to tap into, but the pool of people experienced with LEED in this setting is relatively small. There are just not that many new LEED Green Buildings out there yet.

Our overall project costs were significantly higher than a normal project, and somewhat above projections. On next LEED job would factor in some additional time for design, and for site visits by LEED certification team. LEED verification involved review of plans, plus monitoring during the construction phase and testing of the equipment in action. It worked out well in the end though, the LEED verification team agreed with our interpretations and approved our system design. The feedback from building users has been great.

"This was a very fun project; I got to do a lot of stuff I normally don’t get to do. Incorporating data from occupancy sensors was something new, but easily accomplished within ASI Visual Expert. The biggest technical challenges were to integrate so many inputs, and to balance the different control requirements in a single specification.

The ASI products are well-suited for this type of challenging application. We do the ventilation calculations in the ASIC/2 controller with no performance worries. I believe that other manufacturer's controllers would have been taxed doing these calculations on-board, and in some cases we’d have to rely on the supervisory controller rather than the unitary controller, which would add to project costs." - Peter Lewis, Dual Temp, Allentown, PA