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Ventilation Strategies: Controlling Fresh Air
The first goal when designing an HVAC system is occupant comfort. Comfort includes considering thermal, acoustic (sound), and health conditions delivered by the system. HVAC helps create a healthy environment that is achieved through the delivery of fresh air to the space.
Recognized as a need in the 1960s, ASHRAE documented this with the first publication of standard 62 in 1973. This standard, now known as 62.1, provides the ventilation requirements and guidelines to achieve a well-ventilated building...
VAV Systems: How Air Flows Through the Equipment
The purpose of using a Variable Air Volume (VAV) system is to add controllability to a diversity of occupancies using only one air handling unit. A constant volume system is like what you have in your home, either off or on. If you apply a constant volume system to a space with multiple heating/cooling load profiles, someone will not be comfortable at different times of operation. The fundamental parts of a VAV system include:
- Air handling unit
- Primary ductwork
- Terminal unit
- The ductwork/air distribution...
HVAC Ins & Outs with Dan Int-Hout - Area Factors and Free Area
Every so often, we get a request for the Ak, or area factors, or for the “Free Area” for our air outlets and inlets. For many years, manufacturers published “area factors” for balancing purposes. These Ak factors are determined by measurement of indicated air velocities and measured air quantities and can be used to balance HVAC systems. For a number of reasons, these values, however, are no longer being presented. When we get these requests, the first question we must ask is “What are you going to do with the value”?
VAV Control: Terminal Unit Sequence Affects the Entire HVAC System
Developing real estate requires millions of decisions about what the building will look like, how to fit it within a budget, how will it operate, what HVAC system to use, etc., etc., etc. Each decision has an impact on the final product. One of these small decisions may never be consciously by the engineer designing the mechanical systems. As a junior engineer straight out of college, I was designing mechanical systems as a consulting engineer. This involved listening to the client, performing load calculations, and choosing the equipment to keep the...
HVAC Ins & Outs with Dan Int-Hout - What is wrong with ADPI?
The Air Diffusion Performance Index (ADPI) was developed at Kansas State University in the 1960’s as an ASHRAE project to assist in understanding air diffuser layout and performance. The basic concept is that the ratio of the discharge air projection, defined by the diffuser’s throw, and the separation distance between air outlets, could be used to define the resulting air mixing in a space. The percentage of points in the “occupied zone” in a space that meet a criterion for acceptable “draft temperature” determined the ADPI. An ADPI of 80% was determined...