A psychrometric analysis involves using a psychrometric chart, as seen in Figure 1, to determine the dry bulb (☏), wet bulb (☏), dew point (☏), RH (%), humidity ratio (gr/lb), and enthalpy (btu/lb) of air at a given condition. Museums, hospitals, and lab buildings all generally need stricter temperature and humidity set points, making psychrometric analysis an important step in the design of the HVAC systems that serve these types of buildings. For instance, a typical office building will require a space temperature of 75☏ ± 2☏ and a humidity level of 50% ± 5% however, a typical museum gallery may require a space temperature of 70☏ ± 2° and a relative humidity (RH) of 45% ± 5%. Latent Heat Flow - Latent heat is the heat when supplied to or removed from air results in a change in moisture content - the temperature of the air is not changed.Buildings require various levels of temperature and humidity controls, but when it comes to preserving historical artifacts or performing an operation, the temperature and humidity levels in a space become crucial to keep a building operational.outdoor relative humidity and temperature. Outdoor Relative Humidity and Temperature - Recommended indoor relative humidity vs. HVAC Abbreviations - Commonly used HVAC abbreviations.Heat Recovery Efficiency - Classification of heat recovery efficiencies - temperature efficiency, moisture efficiency and enthalpy efficiency - online heat exchanger efficiency calculator.air temperature and relative humidity - in degrees Fahrenheit and Celsius. Heat Index - Equivalent heat index vs.Great Sensible Heat Factor - GSHF - The Great Sensible Heat Factor is the ratio sensible to total heat in a cooling coil.Cooling Load - Latent and Sensible Heat - Latent and sensible cooling loads to consider when designing HVAC systems.Cooling and Heating Equations - Latent and sensible cooling and heating equations - imperial units.Air Psychrometrics - Moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content.Air Conditioning - Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.Retail, Department Stores - SHR : 0.65 - 0.90.Precision Manufacturing - SHR : 0.80 - 0.95.Police Stations, Fire Stations, Post Offices - SHR : 0.75 - 0.90.Motel and Hotel Guest Rooms - SHR : 0.80 - 0.95.Motel and Hotel Public Areas - SHR : 0.75 - 0.90.Medical/Dental Centers, Clinics and Offices - SHR : 0.75 - 0.85.Malls, Shopping Centers - SHR : 0.65 - 0.85.
Hospital Patient Rooms, Nursing Home, Patient Rooms - SHR : 0.75 - 0.85.Cocktail Lounges, Bars, Taverns, Clubhouses, Nightclubs - SHR : 0.65 - 0.80.Banks, Court Houses, Municipal Buildings - SHR : 0.75 - 0.90.Auditoriums, Theaters - SHR : 0.65 - 0.75.If the SHR value for an evaporator is 75% (0.75) - 75% of the load cools the air (sensible load) and 25% of the loads dehumidifies the air (latent load). SHR = (1.005 kJ/kg oC) (( 26 oC) - ( 20 oC)) / (( 47 kJ/kg) - (3 7 kJ/kg))Ħ0% of the load provided to the room heats the air (sensible load) and 40% of the load provided humidifies the air (latent load). The Sensible Heat Ratio can be calculated as From the Mollier chart the enthalpy of the outlet air is 47 kJ/kg. The outlet temperature is 26 oC and the relative moisture of the outlet air is 40%. From the Mollier chart the enthalpy of the inlet air is 37 kJ/kg. The relative moisture of the inlet air is 50%. The inlet temperature to a room with some people is 20 oC.
H i = inlet moist air enthalpy (kJ/kg, Btu/lb) Example - SHR for a room H o = outlet moist air enthalpy (kJ/kg, Btu/lb) Q t = total heat load - sensible heat and latent heat (kW, Btu/hr)Ĭ p = specific heat air (1.005 kJ/kg oC, 0.240 Btu/lb oF) SHR = sensible heat ratio (ratio of sensible heat load to total heat load) The Sensible Heat Ratio - SHR - is used to describe the ratio of sensible heat load to total heat load and can be expressed as:
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