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. 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. Continue reading “Variable Air Volume Box VAV Box Hot Water Reheat” »
In air conditioning and heating applications it is necessary to accurately measure temperature to offer control of the temperatures relative to the application for which the HVACR equipment is serving. There are four separate temperature scales used to measure temperature and it becomes necessary at times to have the ability to convert between the different scales. The two most common scales used by most people are Fahrenheit and Celsius. Fahrenheit is mostly used in the United States where the culture has resisted changing from standard measurements to the metric system. Celsius is used throughout the world including the United States and Canada. Scientist often use Kelvin and Rankine measuring scales to measure temperature. These temperature scales, Rankine and Kelvin, are uncommonly used in popular culture no matter where you live in the world except by the scientific community and are often used to measure extreme temperatures. Continue reading “Temperature Measurement & Conversion for HVACR” »
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).
This is not a normal commercial boiler stack in this boiler room. It has a bypass stack for an commercial hot water economizer. All boilers have make-up water to make up for water lost in the systems especially for domestic hot water use. This hot water boiler system also served the domestic water needs for the local community where these boilers provided heat. Notice the dampers on the stacks (both the vertical and the horizontal stacks). These are controlled by a direct digital controller, located in the boiler room, and cause the hot gas to be diverted to an commercial hot water economizer instead of outside. Inside the boiler economizer were coils where the cold water supply water from the city was routed. This cold water supply was for domestic hot water use. Domestic hot water use is hot water for showers or the sinks for washing dishes or your hands. The water supplied from the city was typically fifty degrees Fahrenheit. After running through this cold supply water from the city through the boiler economizer the water was almost ninety degrees Fahrenheit. This system saved the organization money by using the heat from the gas stack gases. Instead of dumping it outside where it would be dissipated into the outside air it was routed through the commercial hot water economizer where it pre-heated the cold water supply for domestic hot water use. The commercial hot water economizer will help pay for itself and many other things by making the boiler room more efficient. Continue reading “Commercial Boiler Stack with Economizer” »
This plate heat exchanger is used in a data center for a chilled water system and is a chilled water economizer. Plate heat exchangers are used in marine applications, industrial processes including chemical processing systems, food processing, and many HVAC applications including chilled water applications, hot water applications, and economizer applications. In chilled water applications plate heat exchangers can be used to bypass the chiller when outdoor ambient temperatures are optimal for using the cooling tower for free cooling. Generally, this free cooling mode can only be used with plate heat exchangers when outdoor ambient air temperatures are below 50 degrees Fahrenheit. When plate heat exchangers are used for free cooling the control system uses valves to isolate the chiller from the rest of the loop and the plate heat exchanger is used like a chiller. Continue reading “Plate Heat Exchanger and Free Cooling” »
There are different types of electric heating available in homes but probably the most common use for electric heat other than portable electric heating units is electric heat strips used for back-up heat in heat pumps. Sizing the electric heat strips for heat pump back-up heating applications will depend on many different variables which include the size of the space to be heated, the insulation values of the whole structure including doors and windows, and the geographical location of the dwelling. Typically, heat pumps are more common in southern climate regions where the temperatures in the winter are mild. When the temperature outdoors drops below 38 degrees Fahrenheit the outside heat pump units starts lagging behind on demand to heat the structure so a back-up source of heat is needed to provide heating when the temperature outside drops below this temperature.
The average residential/light commercial boiler typically uses different controls to sequence the boiler. Boiler control in commercial and industrial applications can be very complex and can have added layers of controls outside of the local boiler controls that come from the manufacturer. There are also differences of the controls between steam and hot water boilers. Breaking all this down into sections we’ll be as concise and detailed as possible while using brevity to describe residential/light commercial boiler control and cover commercial/industrial boiler control in another article. Some of this information will overlap but rest assured we’ll be as detailed as possible.