Keep the air filter clean
The easiest way to ensure your system operates efficiently and economically is by keeping the air filter clean. There are several types of air filters and several possible locations for the air filter. Ask your Ruud Reliable Top Contractor where your air filter is located and which type of filter to use.

Keep doors and windows closed
Close all doors and windows to the outside. This will reduce the heating load in winter and the cooling load in summer. Your system will operate more economically as a result.

Keep vents and grilles unobstructed
Arrange your furniture and drapes so that all output vents and intake grilles are free from obstruction. This will reduce the cooling and heating load on your system, providing more economical operation.

Avoid excessive use of exhaust fans
Excessive use of kitchen or bathroom exhaust fans will make your system work harder. This will increase energy consumption and costs. Keep costs in check by making wise use of exhaust fans.

Use the AUTO setting
Generally, it is best to set your indoor fan to AUTO. This costs less and provides better humidity control in the summer. However, if you desire to operate your system with constant air circulation, ask us for advice.

Control direct sunlight
Let the sun in during winter. Keep the sun out during summer. In summer, direct sunlight increases the load on your cooling system. Use of window shades and awnings will reduce the amount of direct sunlight and lower the cooling load. In winter, direct sunlight reduces the load on your heating system. Open window shades and awnings to increase direct sunlight and lower the heating load.

Keep the condenser coil clean
The condenser coil (the unit outside your house) should be kept clean to ensure efficient operation. If the condenser coil becomes restricted by dirt, lint, paper, grass clippings, leaves, or other debris,system efficiency will deteriorate. Use a garden hose to keep the condenser coil clean.

Insulate air ducts
Be sure all air ducts are well-insulated. Ducts should also be sealed with a vapor barrier.

Keep an air tight house
Ensure maximum retention of heated or cooled air by adding insulation to outside walls and to the attic. Seal cracks and use storm doors and/or insulated doors to prevent air leaks.

Properly vent clothes dryers
Be sure your clothes dryer is vented to the outside. Also ensure that your clothes dryer is vented away from your outdoor unit.

Keep heat away from the thermostat
Make sure no heat-generating appliances are near your thermostat. These include lamps, TVs, stereo and computer equipment.

Many state codes also specify minimum energy efficiency requirements, ventilation controls, pipe and duct insulation and sealing, and system sizing, among other factors. In addition, some states and localities have established ventilation and/or other indoor air quality related requirements that must also be followed.

• Design in accordance with ASHRAE standards Design systems to provide outdoor air ventilation in accord with ASHRAE Standard 62.1-2007 (available at www.ashrae.org ) and thermal comfort in accord with ASHRAE Standard 55–1992 (with 1995 Addenda) Thermal Environmental Conditions for Human Occupancy
• Ensure familiarity with, and adherence to, all state and local building codes and standards.

However, sealed buildings with appropriately designed and operated HVAC systems can often provide better indoor air quality than a building with operable windows. Uncontrolled ventilation with outdoor air can allow outdoor air contaminants to bypass filters, potentially disrupt the balance of the mechanical ventilation equipment, and permit the introduction of excess moisture if access is not controlled.

Strategies using natural ventilation include wind driven cross-ventilation and stack ventilation that employs the difference in air densities to provide air movement across a space. Both types of natural ventilation require careful engineering to ensure convective flows. The proper sizing and placement of openings is critical and the flow of air from entry to exit must not be obstructed (e.g., by closed perimeter rooms).

Designers should consider the use of natural ventilation and operable windows to supplement mechanical ventilation.

Consider outdoor sources of pollutants (including building exhausts and vehicle traffic) and noise when determining if and where to provide operable windows.

If operable windows will be used to supplement the HVAC system, ensure that:

• openings for outdoor air are located between 3-6 feet from the floor (head height);
• the windows are adjustable and can close tightly and securely;
• the windows are placed to take maximum advantage of wind direction, with openings on opposite sides of the building to maximize cross-ventilation.

Double-sloped drain pan and drain trap depth

In most parts of the country, climatic conditions require that outdoor air must be heated and cooled to provide acceptable thermal comfort for building occupants, requiring the addition of HVAC systems. The selection of equipment for heating, cooling and ventilating the school building is a complex design decision that must balance a great many factors, including heating and cooling needs, energy efficiency, humidity control, potential for natural ventilation, adherence to codes and standards, outdoor air quantity and quality, indoor air quality, and cost.

Where feasible, use central HVAC air handling units (AHUs) that serve multiple rooms in lieu of unit ventilators or individual heat pumps.

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. Unit ventilators and heat pumps have the advantage of reduced floor space requirements, and they do not recirculate air between rooms. However, it is more difficult to assure proper maintenance of multiple units over time, and they present additional opportunities for moisture problems through the wall penetration and from drain pan and discharge problems. Central air handling units have a number of advantages as compared to unit ventilators and heat pumps serving individual rooms. They are:

• Quieter, and therefore more likely to be turned on or left on by teachers and staff;
• Less drafty due to multiple supplies and a return that is away from occupants;
• Better 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 higher efficiency air filters, and more surface area;
• Made of heavier duty components;
• Less likely to have quantity of outdoor air supply inadvertently reduced.

Specify the following features for all air handling units:

• Double-sloped drain pan – A double-sloped pan prevents water from standing and stagnating in the pan.
• Non-corroding drain pan – Made from stainless steel or plastic. Prevents corrosion that would cause water to leak inside the AHU.
• Easy access doors – All access doors are hinged and use quick release latches that do not require tools to open. Easy access to filters, drain pans, and cooling coils is imperative.
• Double wall cabinet – The inner wall protects the insulation from moisture and mechanical damage, increases sound dampening, and is easier to clean.
• Tightly sealed cabinet – Small yet continuous air leaks in and out of the AHU cabinet can affect IAQ and energy. The greatest pressure differentials driving leaks occur at the AHU.
• Double wall doors with gaskets – Double wall doors provide better thermal and acoustic insulation, and will remain flatter, allowing a better seal against door frame gaskets
• Minimum 2 inch thick filter slots – For better protection of the indoor environment, as well as the equipment and ducts, the filters slots should be able to accommodate 2 in. or thicker filters.
• Extended surface area filter bank – To reduce the frequency of filter maintenance and the cost of fan energy, the bank is designed to allow more filter area, such as the deep V approach or bags.
• Air filter assemblies (racks & housings) designed for minimum leakage – The filter bank should have gaskets and sealants at all points where air could easily bypass the air filters, such as between the filter rack and the access door. Use properly gasketed manufacturer supplied filter rack spacers.
• Air filter monitor – A differential pressure gauge to indicate the static pressure drop across the filter bank. This feature could easily be installed as an option in the field.
• Corrosion resistant dampers & links – All moving parts such as pivot pins, damper actuators, and linkages are able to withstand weather and moisture-induced corrosion for the full life of the system

First cost, energy costs, and moisture control do not have to be at odds with good IAQ. Energy recovery ventilation equipment can make the negative implications of 15 cfm per person of outdoor air behave like 5 cfm, while retaining the IAQ advantage of 15 cfm. This approach has been proven in many schools in various regions east of the Rockies, where advanced HVAC systems cost roughly the same as conventional systems, yet provide significant operating cost savings and IAQ advantages.

EPA has developed the School Advanced Ventilation Engineering Software (SAVES) package as a tool to help school designers assess the potential financial payback and indoor humidity control benefits of Energy Recovery Ventilation (ERV) systems.

Proper location of outdoor air intakes can minimize the blockage of airflow and intake of contaminated air.

Sloped Intake Plenum and Accessible Intake Screen

The bottom of air intakes should be at least 8 inches above horizontal surfaces (generally the ground or the roof) to prevent blockage from leaves or snow. In northern locations, more separation may be needed due to greater snow depths or drifting snow.

• Intakes should not be placed within 25 feet of any potential sources of air contaminants, including sewer vents, exhaust air from the school, loading docks, bus loading areas, garbage receptacles, boiler or generator exhausts, and mist from cooling towers.

If the source is large or contains strong contaminants, or if there is a dominant wind direction in the area, the minimum separation distance may need to be increased. Air admittance valves, an inexpensive and code-approved one-way air valve, can be added to sewer vents to eliminate the potential for release of gases into the surrounding air.

• Grilles protecting air intakes should be bird- and rodent-proofed to prevent perching, roosting, and nesting.

Waste from birds and other pests (e.g., rats) can disrupt proper operation of the HVAC system, promote microbial growth and cause human disease. The use of outdoor air intake grilles with vertical louvers, as opposed to horizontal louvers, will reduce the potential for roosting.

• Intake Screens must be accessible for inspection and cleaning.

In existing schools, an insufficient amount of ventilation air is often the result of clogged intake screens that are inaccessible for inspection and cleaning. Screens hidden by an intake grille should be designed with a grille that is easily opened, such as a hinged grille with two quick-release latches, or in the worst case, a grille with four one-quarter turn fasteners. All screens should be easily removable for cleaning.

• Consider adding a section of sloped intake plenum that causes moisture to flow to the outside or to a drain if intake grilles are not designed to completely eliminate the intake of rain or snow.

If outside air is provided through a mechanical system, then at least 15 cubic feet per minute (cfm) of outside air must be provided for each occupant. A typical classroom with 30 people requires a minimum of 15 x 30 or 450 cfm of outside air.

In spaces where the number of occupants is highly variable such as gyms, auditoriums and multipurpose spaces, demand controlled ventilation (DCV) systems can be used to vary the quantity of outside air ventilation in these spaces in response to the number of occupants. One technique for doing this is to install carbon dioxide (CO₂) sensors that measure concentrations and vary the volume of outside air accordingly. If an auditorium fills up for school assembly, then CO₂ concentrations will increase, a signal will be provided to the HVAC system and outside air volumes will be increased accordingly. When the spaces served by an air handler have highly variable occupancy, this type of control can both save energy and help control moisture (and mold) by reducing the quantity of humid outside air when it is not needed for ventilation. CO₂ and other sensors must be periodically calibrated and maintained.

• Air filters should have a dust-spot rating between 35% and 80% or a Minimum Efficiency Rating Value (MERV) of between 8 and 13.

The higher the rating, the better the protection for the equipment and the occupants. It has been estimated that a 30% increase in static pressure across a coil results in a $200 per 10,000 cfm of air movement (at 7 cents per KWH).  This does not include the added cost of cleaning dirty heating or cooling oils, drain pans, or air ducts. Designers should consider specifying a low efficiency (~10%) pre-filter upstream of the main filters. The pre-filters are generally easy and inexpensive to change, and will capture a significant amount of the particulate mass in the air thereby extending the useful life of the more expensive main filters. See ASHRAE Standard 52.2-1999 Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size  available at www.ashrae.org

Pressure Drop

• Design more filter surface area into ventilation systems.

This has two advantages: the number of filter changes each year is reduced, thereby reducing the cost of labor to properly maintain the filters; and static pressure loss is lower, which saves money by reducing the amount of power needed to operate fans and blowers. Since different filter media are approximately proportional in their efficiency/pressure drop ratio, the most effective method for reducing pressure drop is to design more filter surface area into the filter system. This can be done by the specification of a filter with larger amounts of surface area, such as a pleated filter or bag filter. The next method is to increase the number and/or size of the filters in the airstream, for example, by mounting the filter slots in a “V” pattern, rather than a filter rack that is simply flat and perpendicular to the airstream.

Monitoring Pressure

• Consider installing a simple pressure differential gauge across all filter banks.

This will prevent school facilities personnel from having to guess whether the filter is ready for replacement. A gauge with a range of zero to 1.0 in. w.g. can save money and the environment by preventing premature disposal of filters that still have useful life, and can prevent health and maintenance problems caused by overloaded filters that have blown out. The gauge should be easily visible from a standing position in an easily accessed location near the air handling unit.

Outdoor Air Volume Monitoring and Control

Supplying acceptable quantities of outdoor air to occupied spaces is a critical component of good indoor air quality. Yet nearly all school ventilation systems cannot indicate whether outdoor air is even being supplied to the school, much less gauge the quantity of that air. Virtually all existing school ventilation systems rely upon a fixed damper to regulate the amount of outdoor air. Yet wind, stack effect, unbalanced supply and return fans, and constantly changing variable air volume (VAV) systems can cause significant under- or over-ventilation, which can affect IAQ and energy costs. Combinations of these effects can even cause the intake system to actually exhaust air.

• Specify the addition of a measuring station that actively controls the amount of outdoor airflow by modulating the outdoor air damper and the return (recirculation) damper, if needed to overcome wind and stack effects.

These measuring stations are designed to work in limited duct space and with low air velocities. This is an easy task, as some manufacturers offer their airflow measuring stations in separate packages with dampers and actuators, and others are built into the AHU at the factory.