Jun 21, 2016 -- K-12 schools are one of the most important projects engineers can manage. It demands a unique HVAC system, including unique Building Envelope and Air Quality. Kindergartens through high school buildings in the U.S. spend an average of 67 cents/square foot (ft2) on electricity and 19 cents/ft2 on natural gas annually.
In a typical school building, lighting, space heating, and water heating represent between 74 and 86 percent of total use depending on climate, making those systems the best targets for energy savings Energy accounts for about 2.2 percent of a school’s expenditures. Although this represents only a small percentage of total costs, it is one of the few expenses that can be decreased without affecting classroom instructions.
America ends up spending more than $7.5 billion a year on energy than on textbooks. It has become inevitable for schools to gain control over their utility costs. However, school district juggles a lot to budget aptly for operation, maintenance, as well as capital projects.
Accumulation of several maintenance activities lead to higher energy costs and further equipment malfunctions. Due to lack of preventive maintenance, operational life of building equipments drop down in no time leading to immediate investment in costly retrofit measures. Nevertheless, facility condition is given due importance and is considered important for student learning as well. Lawsuits regarding less or no funding for education has forced authorities to focus more on condition of school building too, then just students.
A large number of Educational Buildings are expected to undergo retrofit. Now, to determine energy consumption, an energy simulation must be performed for quantifying the energy consumption characteristic of HVAC system and assessing the same for further benefits. Lighting is also an area to be focused for new as well as retrofit buildings.
12th October 2011, the American Society of Heating, Refrigerating and Air-Conditioning Engineers ( ASHRAE) released its “Advanced Energy Design Guide for K-12 School Buildings” to offer best practices for architects, design engineers, energy modelers, general contractors, facility managers and building operations staff. Over 30% of energy is consumed by Lighting in a school building and in order to bring down the energy consumption, the school must pay attention to improvise the Lighting and HVAC strategy of the school building.
HVAC Strategy for School Building
There is no just one solution pertaining to HVAC for system, as all schools operate on different grounds. A well designed HVAC system is equipped to keep up the space temperature and humidity conditions, as well as minimum outdoor air amounts, economically and efficiently.
ASHRAE standard 62.1-1999 mentions that each person in a classroom receive 15 cu. ft. per minute of fresh air, and a classroom with 30 people requires a ventilation rate of about 450 cfm. Factor in a school’s age, size, construction - such as walls, lights, doors and windows - zone requirements and the climate where the school is located, and it’s easy to see why schools present unique challenges for meeting HVAC requirements. The key is in knowing how to balance all the elements of the equation.
Using central HVAC air handling units (AHUs) that serve multiple rooms in lieu of unit ventilators or individual heat pumps is one of the solutions. Although there are many different types of air handling units, for general IAQ implications in schools, air handling units can be divided into two groups: unit ventilators and individual heat pump units that serve a single room without ducts; and central air handling units that serve several rooms via duct work.
Central air handling units benefits more in terms of:
- Quieter and therefore more likely to be turned on or left on by teachers and staff;
- Less drafty due to several supplies and a return that is away from occupants;
- Enhanced at controlling humidity and condensed moisture drainage;
- Easier to maintain due to reduced number of components and few units to access;
- More space around units and can be accessed without interfering with class activities;
- Space for greater competence air filters and more surface area;
In addition to "atmospheric dust," airborne particulates can include pollen, mold (fungal) spores, animal dander, insect proteins, pesticides, lead and infectious bacteria and viruses. Designers can incorporate features into the ventilation system that can help school occupants as well as the efficiency and longevity of the HVAC system. In addition, these features can reduce the need for expensive cleaning of the duct work and air handling units.
Filter Efficiency: Air filters must ensure a dust-spot rating between 35% and 80% or a Minimum Efficiency Rating Value (MERV) of between 8 and 13. The higher rating denotes the better protection for the equipment and occupant. Even 30% increase in static pressure across coil can cost the school$200 per 10,000 cfm of air movement (at 7 cents per KWH). And this in non-inclusive of the additional cost of cleaning dirty heating or cooling oils, drain pans, or air ducts.
HVAC Designers must consider specifying a low efficiency (~10%) pre-filter upstream of the main filters. These pre-filters are usually easy to maintain and low-cost to change and will capture a substantial amount of the particulate mass in the air thus ranging the valuable life of the more expensive main filters.
One established notion of attaining energy efficiency in HVAC systems is to design systems that use novel configurations of current system mechanisms. Latest research has confirmed that an amalgamation of prevailing air conditioning technologies can bid effective HVAC solutions for energy preservation and thermal comfort.
In this Article we have discussed just HVAC strategy for school building, while there is more to the Lightning analysis too. We will investigate and discuss their potential to improve the system performance in our forthcoming articles about commissioning and lighting analysis.
Let’s not forget the other factors such as climatic conditions, expected thermal comfort, initial and capital cost, the availability of energy sources and the applications are responsible for the building performance and affects it simultaneously as well.
Bhushan Avsatthi is a BIM expert, a certified Sustainable Building advisor, and an associate director with more than 15 years of industry experience. He leads a team of architects, Structural & MEP engineers, LEED consultants and energy modelers. Bhushan strives to make his organization a cohesive resource for sustainable building design. He regularly participates in green initiatives like tree plantations, and promotes using bicycles for everyday commute.