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Glass &Windows Selection



In houses and some very old buildings you still find radiators for heat, and windows for ventilation and cooling. Most modern office buildings have replaced radiators and openable windows with heating, ventilating, and air conditioning (HVAC) systems. These systems consist of ductwork to transport air and fans to push or pull it through the ductwork. The openable windows have been replaced by dampers or louvers on the fan housings which open to bring some fresh air into the system. A thermostat calls for heating or cooling to maintain the temperature. The air is transported to all the rooms through the ductwork and blown into each room through the diffusers to both ventilate and maintain the desired temperature.

The ventilation system is very important to how you feel when you work in the building as well as to whether you are warm enough or cool enough. The perfumes and shampoos that people wear, the materials that we use in very small amounts like whiteout or glue, residues from cleaning compounds, the new furnishings and carpeting, even our exhaled breath impacts the air around us. We need the ventilation system to keep the levels of these contaminants, byproducts of normal routine, to a minimum. This is done by constantly bringing in fresh air and removing stale air. For particular sources of contamination like a heavily used photocopy machines, we cannot depend on this "general" ventilation system but should have a local exhaust system which takes the pollutant away before it can get into the air which surrounds us and recirculates.


Air enters the building through the outdoor air intake. This may be on the roof in a roof-mounted unit or it may be in the wall of the fan room. Amounts of air coming in are usually controlled by dampers which can be adjusted to take in more or less air depending on the outside temperature. In order to get adequate ventilation, the dampers should be adjusted so that they can never completely close. A minimum setting which allows for 25% of the air to be outdoor air is recommended. (Since the energy crisis, the start of indoor air quality problems in many buildings, air intakes have been set to take in 10% or less to save on heating and cooling costs.)

Common problems with intakes:
· There are none. No fresh air is coming in. There should be at least 20 cubic feet per minute (cfm) of fresh outside air per occupant coming into each space.
· The intake is poorly located and brings in contaminated air.
· The intake dampers are sealed shut.
· Pigeons are roosting in the fresh air intake.


This fresh air mixes with air returning from the rooms and this mixture then passes through one or more filters. The first filter will usually be a fiberglass filter that catches leaves and feathers and large dust. Small particles or fine dust may pass right through as will gasses like car exhaust fumes. There may be other filters to catch finer dust or even to catch volatile organic carbons (VOCs) but often there is just one filter for large particles.

Common problems with filters:
· The filters are not changed regularly or often enough. Should be done at least quarterly.
· The filters are not the right type to remove contaminants that are coming in.


The fans with their motors move the air. If they do not have sufficient capacity they will not bring in enough air. If the fan is not working properly the air doesn't move, or not enough of it moves.

Common problems with fans:
· Fan belts are broken or slipping, fan blades corroded, motors burned out
· Additions have been made to the system but the same fan is still trying to run it and is not strong enough.


The air is forced by the fans along the ducts to the diffusers which allow the air into the room. Within the room the air should mix thoroughly so that the temperature is the same throughout the room and fresh air mixes in. Good mixing is essential for good temperature control as well as freshness.

The air should then leave the room through the return. They may look similar, but the air comes in through the diffuser and leaves through the return. Use a piece or tissue paper to test these. The tissue should stick to the surface if the air is being drawn out and wave if the air is blowing into the room.

Common problems with ducts and diffusers and returns:
· The ducts have been damaged and are no longer connected to the fan.
· The ducts are lined on the inside with fiberglass which is breaking down -The ducts may have accumulated large amounts of dust or have become damp and grown mold or bacteria which is then distributed with the air
· The ducts are delivering more air to the rooms that are close to the fan and much less to the rooms that are at the end of the line.
· Some rooms lack diffusers or returns completely because walls and partitions have been changed but the ventilation system was never changed.
· Diffusers have been blocked off, often to change temperature.
· Returns have been blocked, often thoughtlessly, by furniture and stuff.
· Proper air mixing is not occurring because diffuser and return are close together and the air goes straight from one to the other.
· The return air does not have a duct to carry it but passes instead through the open space above the dropped ceiling. Whatever is up there, asbestos, pigeons or former pigeons, is swept right into the HVAC system and recirculates.


Somewhere in the system, usually near the fan the will be the means of heating or cooling the air. The cooling system is usually some metal coils containing chilled water or a refrigerant which are inside the duct. The air passes over these cold coils and is cooled. The air also leaves some moisture in the form of condensation on the coils. There should be a pan underneath to catch the drips and the pan should have a drain so that it does not accumulate water. Some form of heat like an electric heater or hot water coils or other heated surface may also be found inside the duct to heat the air when necessary. The air may also be humidified for comfort in the winter.

Relative humidity affects comfort. The official comfort range is between 30 and 60 percent with temperatures between 68 and 80oF. This doesn't work for everyone.

Potential problems with the heaters and coolers:
· Water accumulates in the condensate drip pan, mold grows, and gets into the air.
· The heating or cooling coils get dirty, cutting down air flow and adding dirt to the airstream.
· Refrigerant can leak into the air system
· Flue gas, products of combustion, can leak into the air system.


Some types of systems, called variable air volume (VAV) systems, have extra thermostats and dampers above the diffusers. If a room or group of rooms is already at a satisfactory temperature, the dampers will close and not allow that room to get any more air. Others will have a constant flow of air but vary the mixture between return and fresh or the use of heat and cooling.

Common problems with the whole system:
· It is turned on and off by a timer and starts at, say 8, turns off at, say, 5 and people who work other hours have no ventilation.
· Nobody knows where the components of the HVAC system are or how it works.
· No one has checked it since 1948. The last time it was balanced was when the building was built and many changes have occurred since then.




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