Variable Air Volume Box with Hot Water Reheat - The variable air volume box or VAV box is a commercial solution to adding multiple zones to large buildings. VAV boxes offer zoning solutions so that separate zoning demands or temperature selections can be maintained in different areas of the building. If the president of the company wants the temperature in their office to be 70 degrees Fahrenheit but the vice president wants their office to be 74 degrees Fahrenheit then it is possible with the VAV zoning system as long as their VAV boxes are on different zones.
Variable Air Volume Box with Hot Water Reheat
This particular VAV box in the picture is not fan powered. It relies on the main VAV air handling unit to provide all the air. Generally, when a fan powered VAV box is calling for heat the damper inside the VAV box closes down so that minimal CFM’s are coming through the primary duct from the air handler. The fan turns on an pulls air from the plenum space above the ceiling. This plenum air is normally warmer than the air inside the occupied space. The heating system kicks in and adds heat to the air until a setpoint is attained. The heat for a VAV box can typically be a hot water coil or electric heat strips. The VAV box in the picture has hot water reheat.
Variable Air Volume Box with Hot Water Reheat
This chilled water unit is a new ammonia chiller. This unit is also unique in that it has no compressor. Instead it uses the chemical properties of ammonia and heat from natural gas to condense the refrigerant which is ammonia. A chiller provides chilled water to a chilled water loop. Cold water is circulated through a loop where it is direct into a coil in an air handler. Air is blown across a coil where a heat exchange process takes place. The air handler discharges cool conditioned air throughout a duct system. Chilled water systems are typically used in commercial air conditioning applicationsbut there are some chilled water systems in residential applications. Continue reading
VAV Air Handlers are ideal for providing zones in a commercial building. Office space typically has several offices and open areas that need to be conditioned for the comfort of the people working in those areas or offices. By installing VAV boxes and zoning the duct work from those VAV boxes these areas and offices can be kept comfortable using a VAV air handler system. Each box can have its own thermostat and that area or office served by that particular VAV box can be maintained and conditioned for the people working in that space. The VAV box will receive its conditioned air from a VAV air handler through a primary duct that feeds air to the VAV box. The VAV box then determines the amount of air to the secondary duct by a damper located in the VAV box. Depending on what the thermostat temperature set point is and the temperature in the space will determine the amount of air flow the space will receive from the VAV box. Additionally, A VAV box with reheat will energize the heat strips or open the actuator for the hot water coil if the set point and room temperatures calls for the reheat to provide heat to the space (If the VAV box is equipped with reheat).
DDC Controlled Chilled Water Actuator
This chilled water actuator is attached to a valve which supplies chilled water to the air handling unit chilled water coil. The actuator modulates the valve based on a set point inside the DDC program. If the program has trim and respond capabilities the set point will rise up and down based on demand from the VAV boxes or the HVAC zones. Most DDC controlled actuators work off of a DC volt or current signal. The common chilled water actuator motor is generally powered by 24 volts AC. The actuator has the ability to modulate by the DC signal. If the chilled water actuator is a 0 to 10 volt actuator a zero volt DC signal the actuator would be closed if it is a normally closed valve* (*depending if the actuator is normally closed or normally open). If the chilled water actuator gets a 5 volt signal then the actuator will move the valve to a fifty percent position. Therefore, if the chilled water actuator got a 10 volt DC signal it would open 100 percent if it is a normally closed valve. Other actuators work off of a milliamp signal. 0 to 20 milliamps or 4 to 20 milliamps are the usual milliamps signals that will modulate the valve. Other voltage ranges for mudulating an actuator are 2 to 10 volts DC and 0 to 5 volts DC. Continue reading
Air Handler Unit Components: Hot Water Coil Heat
Hot water coils inside of air handler units combine a boiler system or a special capacity hot water heater and forced air to provide forced-air heating. The concept is simple and used a lot in commercial and some in residential. Commercial systems almost exclusively use a boiler to provide hot water to the hot water coil inside the air handler unit while the residential systems use mainly special capacity hot water heaters to provide hot water to the hot water coil inside the air handler unit. On a call for heat a pump is energized to begin the circulation of hot water from the heating source to the coil. The air handler unit blower motor energizes and air begins to move across the coil. Heat is exchanged from the hot water coil to the air and the air is delivered to its appropriate destination through the ductwork.