Educational experience: HVAC systems and energy efficiency in K-12 schools
- Robert J. Linder, PE, LEED AP, Senior Project Manager, Karges-Faulconbridge Inc., St. Paul, Minn.
- Robert N. Roop, CPD, LEED AP, Principal, Peter Basso Associates, Inc., Troy, Mich.
- Abbas Shirian, PE, CGD, LEED AP, Principal-in-Charge, Lead Mechanical Engineer, Bridgers & Paxton Consulting Engineers, Albuquerque, N.M.
CSE: Energy efficiency and sustainability are often the No. 1 request from building owners during new building design. What is your experience in this area?
Roop: Energy efficiency and sustainability are the two hottest topics in the K-12 market today. Many districts in our area are filled with antiquated buildings using technology developed in the early part of the last century. There is very little else from that time period still in use, and even less still being applied in new construction. Since these districts see how inefficient their facilities are, and are faced with shrinking O&M budgets, now more than ever we are asked to consider efficiency and sustainability in not only new construction but also renovation projects. Also, since no one building type has a longer service life historically than K-12 schools, these buildings are optimally suited to take advantage of the return on investment of more efficient, more sustainable, longer life products and systems.
Shirian: Many school districts have mandates that new buildings and major renovations be LEED certified or Energy Star rated, but O&M departments commonly resist the use of systems and equipment that are new or increase maintenance requirements. Consequently, we focus on simple and reliable sustainability concepts such as energy-efficient lighting, daylighting controls, occupancy sensors, low water use plumbing fixtures, high seasonal energy efficiency ratio (SEER) equipment, and controls to allow shutting down spaces that are not in service.
CSE: What unique HVAC requirements do K-12 school structures have that you wouldn’t encounter on other structures?
Shirian: Personnel on site at K-12 schools commonly have a very limited understanding of mechanical and control systems, so we try to design systems tailored to the capabilities of the staff on site. Larger school districts commonly have centralized maintenance staffs with greater technical skills, but they can get overwhelmed performing seasonal changeover. We try to use systems that minimize the maintenance required for seasonal changeover.
Roop: Apart from the unique characteristics of school buildings when compared to other building types, which makes them unique enough, perhaps the biggest challenges are in the lower elementary spaces. Preschool and kindergarten children spend a great deal of time on the floor and so space conditioning starts at the floor level there, unlike the traditional occupied zone of office buildings or other occupancies.
CSE: What indoor air quality (IAQ) challenges have you recently overcome?
Roop: We designed new and renovated facilities for an owner with an IAQ program requiring outside air quantities 30% above those required by code and ASHRAE. To minimize the impact of this increased outside air load on the heating and cooling plants, we supplied a measured quantity of outside air to each space though a variable volume air terminal unit coupled with space CO2 sensors. This demand control ventilation strategy increased the outside air quantity from the code minimum only when space CO2 levels rose above a fixed offset quantity from the levels found in outside air.
Shirian: For conventional HVAC systems, such as VAVs serving multiple zones, we specify air handling system with IAQ dampers and COe sensors. For decentralized HVAC systems like heat pumps and/or fan coil unit systems, a separate dedicated outside air system (DOAS) may be the only reliable method of meeting ASHRAE Standard 62. It is also the simplest method.