Arkansas HVACR NewsMagazine November 2018

S tate, National, Chapter News Tech News

capacity at a set of conditions would produce 21,000 BTUs of sensible cooling and 9,000 BTUs of latent removal because 30,000 x 0.7 = 21,000 and the rest 30,000 x 0.3 = 9,000. Higher SHR (closer to 1.0) = More change in temperature and less humidity removed Lower SHR = less change in temperature and more humidity removed In the HVAC industry, there is a set of standard conditions used to compare one piece of equipment to another. When a system has an SHR rating listed it would often be at AHRI conditions unless the specs state

SENSIBLE HEAT RATIO (SHR)

By Bryan Orr, HVAC School

Every piece of air conditioning equipment is capable of moving a certain amount of heat BTUs (British Thermal Units) at set conditions. In most cases during the cooling mode, a portion of those BTUs will go toward changing the temperature of the air and a part will go towards changing vapor water in the air into water that collects on the evaporator and then drains out. The BTUs that go towards changing the TEMPERATURE of the air are called SENSIBLE and the ones that go toward removing water from the air are called LATENT . The percentage of the capacity that goes toward sensible cooling at a given set of conditions for a given piece of equipment or space is called SENSIBLE HEAT RATIO (SHR). So a system that has an SHR 0f 0.70 and 30,000 Total BTUs of

otherwise.

When doing a load calculation a good designer will calculate and consider the internal and external latent and sensible loads and match up with equipment accordingly based not only on one set of design conditions but on the range of seasonal and occupant conditions that the structure is likely to experience based on the use, design and climate. By following ACCA (Manual J & S) and ASHRAE (62.2 & 62.1 for example) standards a designer will have guidelines to