Ventilating a Zoned Office Building: How Requirements for One Area May Differ From the Next
A zoned heating and cooling system for your office building is an effective way to ensure that your indoor spaces receive the temperature control they need at the most economical level possible. An important factor to keep in mind about zoned systems is that each zone may need different levels of ventilation, even at the same time of day. When planning or revising methods for ventilating a zoned office building, make sure the equipment can accommodate different, sometimes even opposite, requirements for each area in your zoned system.
What Zoned Heating and Cooling Does
A zoned heating and cooling system allows you to divide your office building’s indoor spaces into different areas, or zones, that receive different amounts of heating or cooling, depending on needs. A vacant office, for example, will not need as much conditioning as an occupied one. An office with only a few occupants will have different temperature needs than one with several individuals working within it. A zoned HVAC system uses a series of independent thermostats and motorized dampers to control the amount of heating and cooling that enters a particular zone. In this way, energy consumption is reduced and costs are kept to a minimum.
The Need for Ventilation
Commercial buildings, especially those with tight seals, need plenty of ventilation to keep indoor air quality high. Properly ventilating a zoned office building reduces airborne contaminants such as dust, pollen, fibers, microorganisms and other particulates. It also helps curb odors by either diluting the odors or removing them at their source. Without proper ventilation, indoor air will be stuffy and dirty and can contain material that may aggravate or cause asthma, allergies, respiratory troubles or disease. An accepted industry standard for proper ventilation is ANSI/ASHRAE Standard 62-1999, which calls for 15 to 20 cubic feet of ventilation per minute per person occupying the space.
Zoned Systems and Ventilation
Ventilating a zoned office building requires consideration of the separate requirements of the heating and cooling zones throughout the structure. Since zones are created to be distinct areas with different heating and cooling needs, it makes sense that individual zones will also have different ventilation requirements. These requirements could be the opposite for adjoining zones during the same period or for office areas that are used for different functions. HVAC zoning systems and equipment should be set up in advance to accommodate these diverse requirements.
Zoned ventilation can be further improved by using demand-controlled ventilation systems. These types of systems are designed to react to the number of people in the zone, adjusting ventilation according to how many occupants are in the zone at a given time. They typically use carbon dioxide sensors as part of the control system; higher amounts of carbon dioxide will exist in zones where there are more people. One sensor in the return air ductwork and one sensor per high-occupancy area will usually be sufficient to achieve proper control. When fewer people are in these areas, the system will reduce ventilation rates, which will decrease energy consumption and cost.
When outside ambient temperatures are at the proper level, economizers can be used for ventilating a zoned office building. HVAC-based cooling can be reduced by using higher levels of ventilation through economizers. Cool outdoor air can still be used during heating season to accommodate the cooling needs of any interior zones. When using economizers, reduce the amount of ventilation reaching zones that require heating to the lowest amount possible to keep indoor air quality at acceptable levels. Decreasing ventilation volumes in these cases also helps trim energy costs by reducing the amount of cool air that needs to be heated before it’s distributed to the indoor zones.
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