Most K-8 schools are low-rise structures of medium size with a central core area for offices and administration, and wing-type construction for classrooms. There is usually a small gym with little or no seating; and, depending on the immediate growth in the area, there may also be a number of classroom trailers required prior to and during construction of school additions. Teaching approaches keep changing from individual classrooms to open-plan layouts and back again: open-plan schools have portable partitions that are changed frequently. Due to the ever-changing teaching approaches and layouts, the HVAC system design must be flexible in order to accommodate all of it.
The key building energy systems' electrical loads are lighting and HVAC systems. Cafeteria loads - cooking, ventilation, lighting and even water heating - can be significant in some areas, depending on the availability of natural gas. And with the advent of computers, office equipment is a rapidly increasing load for many schools - especially for those that administer individual laptops to their students during the school year. Nevertheless, most electricity is still consumed in the lighting and cooling systems.
- Construction materials (glass areas, insulation, etc.) and orientation to the sun
- Occupant use and maximum occupancy characteristics (especially time of day)
- Lighting levels and lamp source efficiency (which affects the cooling and heating loads)
- The time and seasonal vale of fuel and power use in building design alternatives
- Floor loads for office equipment and specialized lighting
- Availability and price of water for potential cooling system use
- Most schools are very similar in their design, so, with the exception of schools with kindergarten to fourth grade, which may require heated floors; HVAC equipment should be simple to operate and require no skilled personnel.
Schools are typically designed for a long life under difficult occupancy conditions and tend to be of high quality construction. Due to bond issues and funding with scarce tax dollars, the desire for visible amenities predominates. During original construction, energy conservation and recovery concepts that raise the first cost, but lower O&M and life cycle costs are difficult to justify. However, energy retrofits for the lighting and HVAC systems have successfully been promoted with some of the savings going towards amenity improvements - e.g. a school might get new lights and new Smart Boards with the savings from the energy retrofits - this is known as performance contracting.
The HVAC systems will vary widely and are largely dependent on the size, age, and geographical location of the school. In past years, ventilation-only dominated; however, most new schools are air conditioned. The current trend is to use central or rooftop systems for administrative and common areas, and PTAC or geothermal heat pumps with individual controls for the classrooms. In climates with low heating loads, electric resistance heating is often used for the primary or secondary (for heat pumps) heating source. This design maximizes scheduling flexibility for the off peak uses, like PTA meetings, parent/teacher conferences, and other school meetings.
The gymnasium and cafeteria usually require their own systems, because of their unique loading characteristics. Cafeterias may have heat pump water heaters or heat recovery water heaters included in their systems.
Proper ventilation is necessary to control odors and avoid "sick building" syndrome. Provisions should be made to shut any outdoor air dampers when individual zones or rooms are unoccupied. Many areas have stringent codes regarding fire, smoke, building design, ventilation, and noise control. In many cases, noise production and protection from vandalism must also be considered. As an alternate to roof-top equipment, geothermal heat pump systems are increasing in popularity as they have no outdoor equipment to create noise or be damaged.
Energy Saving Recommendations
Energy conservation concepts should be simple: cooling interior spaces with outdoor air-using economizer cycles, night setback in individual areas, and outdoor air damper control during the system shutdown at night. Water-loop heat pump systems may also be used to conserve energy if the building has significant interior zones. In fact, it may be possible to justify upgrading to higher-efficiency equipment, or even a complete redesign to geothermal heat pumps, as existing HVAC equipment ages and must be replaced. Some designs combine thermal storage, where excess heat generated during the day is stored and used for heating at a later time.
Service water heating is needed for janitorial work, restrooms, cafeterias, and occasionally for shower rooms and swimming pools. Cafeterias, shower rooms and swimming pools usually have their own water heating systems due to loading and temperature characteristics. Hot water used in cafeterias is about 70% of that usually required in a commercial restaurant, but can still be estimated with the same method used for restaurants. Where NSF sizing is required, follow Standard 5.
Provision may be required to supply 180ºF sanitizing rinse, depending on the type of chemicals used in the dishwashing systems. If this is required, a booster heater must be sized according to the temperature of the supply water - usually 140ºF - and the required flow of the dishwasher.
A separate water heating system for swimming pools can be sized as outlined in the section on Swimming Pools\Fitness Clubs.
Energy Saving Recommendations
Most energy conservation measures regarding water heating in schools will be about supplementing cafeteria water heaters with either heat pump water heaters - located in the cooking area - or heat recovery water heaters attached to the refrigeration systems. If a central water heater is used for restrooms, then point-of-use water heaters will also provide good payback. Please refer to the Water Heating section for more detailed assistance.
Food in schools is typically served Cafeteria-style and consumed by students and teachers who take their trays to indoor or outdoor tables. However, pre-planned meals with menus published in advance are becoming more prevalent.
Energy Saving Recommendations
The predominant energy source for school food service has trended toward natural gas. However, some school systems are realizing the overall benefit of electric cooking due to ventilation reductions and personal comfort of the cafeteria staff. Please refer to the Food Services section for additional assistance regarding electric cooking options.
Most of the space in schools is dedicated to classrooms. A typical classroom design will accommodate class sizes of up to thirty students. There will usually be a Smart Board and/or whiteboard on one or more walls, and there may be windows to provide natural light in the room.
In elementary schools, students spend most of their day in the classroom, writing and reading. Adequate light levels of 50 to 100 footcandles are needed for both the horizontal work surface of desks and the vertical plane of whiteboards and computer screens. The individual school often sets the standards for the minimum acceptable number of horizontal footcandles required in a classroom.
Today, many classrooms have flexible seating around tables or designated areas of the room that the teacher sets aside for specific activities. This means that many of today's classrooms require a flexible lighting system that doesn't dictate the placement of desks.
Energy Saving Recommendations
Classrooms for special purposes like science, art, or engineering may require special task lighting. Therefore, it is imperative that uniform light levels, and lamp sources with 3500K to 4100K color temperatures and at least 70 CRI are used. T-8 fluorescent lamps, especially triphosphor types, are an ideal choice.
Classrooms with high ceilings are good candidates for a suspended direct/indirect combination fluorescent fixtures, which significantly reduce the glare on work surfaces. Lower ceilings will require either surface-mounted or recessed fixtures; however, recessed fixtures may be better in this situation, because they're less obstructive. If the classroom is a computer lab, then use high VCP fluorescent fixtures to ensure good glare-control. Providing flexible switching, such as partial fixtures or partial lamps per fixture is recommended. This allows for lower light levels while watching movies or using other audio/visual equipment.
Most lighting efficiency upgrade opportunities will range from upgrading T-12 to T-8 fluorescent and incandescent lightbulbs, to installing LED exit signs. Older gymnasiums may be lighted with incandescent or mercury vapor and thus offer upgrade potential to pulse-start metal halide. Conversion to the pulse-start metal halide can also be justified for some older metal halide systems.
Energy Management systems (EMS), especially Direct Digital Control (DDC) systems, are the most practical options for scheduling before- and after-hour events. Traditionally, HVAC systems are left running or are not available at all for special events, and lighting systems may be left on overnight if a special interest group has their meeting and walks away without switching things off. Thus, simple EMS systems should be located in the school maintenance and/or administrative office where lights and HVAC can be scheduled and controlled.
The trend in school electrical system designs is to place a new service and utility meter in each addition. The original school likely had at least two meters - one for the school and one for the gymnasium. It may be in the school's best interest to use a primary meter to reduce electric cost.