Cooling load temperature difference calculation method
- 1 CLTD/CLF/SCL Cooling Load Calculation Method
- 2 History
- 3 Application
- 4 Explanation of Variables
- 5 Equations
- 6 References
CLTD/CLF/SCL Cooling Load Calculation Method
The CLTD/CLF/SCL (Cooling Load Temperature Difference/Cooling Load Factor/Solar Cooling Load Factor) Cooling Load Calculation Method was first introduced in the 1979 ASHRAE Cooling and Heating Load Manual (GRP-158)  The CLTD/CLF/SCL Method is regarded as a reasonably accurate approximation of the total heat gains through a building envelope for the purposes of sizing HVAC equipment. This method was developed as a simpler calculation alternative to difficult and unwieldy calculation methods such as the Transfer Function Method and the Sol-air temperature Method.  Error when using the CLTD/CLF/SCL method tends to be less than twenty percent over and less than ten percent under. 
After its introduction in the 1979 ASHRAE handbook, research continued on increasing the accuracy of the CLTD/CLF Method. Research completed in 1984 revealed some factors which were not accounted for in the original publication of the method; these findings were a result of the ASHRAE Research project 359. In 1988 ASHRAE Research Project 472 worked to correct these oversights with the introduction of a classification system for walls, roofs, and zones. Additionally, a weighting factor database was generated to help correct for previous inaccuracies. Additional research in Thermal radiation and appliance heat gain with respect to CLTD data was also completed shortly after the original publication of the method. The advancements in each of these areas inspired a revision/compilation effort, and in 1993 the CLTD/CLF/SCL Method was succinctly compiled by Spitler, McQuiston, and Lindsey. 
The CLTD/CLF/SCL Method utilizes pre-determined set of data to expedite and simplify the process of cooling/heating load approximation. The data is divided into many different sections based on many different variables. These variables include, building material of the envelope, thicknesses of the building materials, day of the year, time of day, orientation of the surface (e.g. wall or roof, 90 degrees or 180), and wall face orientation (cardinal directions, i.e. N, NW, S, SE, etc), to name a few. In order to determine which set of CLTD/CLF/SCL data to look at, all the requisite variables must be defined. 
The respective tables of data were generally developed by using the more complex Transfer Function Method to determine the various cooling loads for different types of heating.   The results gained by doing so are then normalized for each type of heat gain used for the tables, CLTD, CLF, and SCL. 
Explanation of Variables
The first of the cooling load factors used in this method is the CLTD, or the Cooling Load Temperature Difference. This factor is used to represent the temperature difference between indoor and outdoor air with the inclusion of the heating effects of solar radiation.  
The second factor is the CLF, or the Cooling Load Factor. This coefficient accounts for the time lag between the outdoor and indoor temperature peaks. Depending on the properties of the building envelope, a delay is present when observing the amount of heat being transferred inside from the outdoors. The CLF is the cooling load at a given time compared to the heat gain from earlier in the day.  
The equations for the use of the data retrieved from these tables are very simple.
Q= heat gain, usually heat gain per unit time
A= surface area
CLTD= cooling load temperature difference
SCL= solar cooling load factor
CLF= cooling load factor
SC= shading coefficient
For heat gain through walls, doors, roofs, and windows (only window conduction):
For heat gains due to people, equipment (hooded and unhooded), and lighting:
For solar heat gains through windows and glazed surfaces:
In addition to tables published by ASHRAE for select latitudes, a computer program called CLTDTAB, available since 1993, can be used to generate custom CLTD/CLF/SCL tables for a specific zone type for any latitude and month. This allows the use of this method, without interpolation, for any area in the world. 
If the program CLTDTAB is used, the results obtained using this method will tend to be very close to the more rigorous TFM Method mentioned earlier. 
- ^ a b c d e f g h i j k l m Spitler, J.D., F.C. McQuiston, K. Lindsey. 1993. The CLTD/SCL/CLF Cooling Load Calculation Method, ASHRAE Transactions. 99(1): 183-192.
- ^ a b McQuiston, F.C., and J.D. Spitler. 1992. Cooling and heating load calculation manual. Atlanta: ASHRAE
- ^ Matalas, Gintas P. 1972. Transfer Function Method of Calculating Cooling Loads, Heat Extraction And Space Temperature, ASHRAE Journal. Vol. 14, No. 12: 54-56.
- ^ Lindsey, K. 1991. Revision of the CLTD/CLF Cooling Load Calculation Method. M.S. thesis, Oklahoma State University.
- ^ a b c d e f g McQuiston, Faye C., Parker, Jerald D., Spitler, Jeffrey D. Heating, Ventilation, and Air Conditioning: Analysis and Design, p216-278. 2005, John Wiley and Sons, Inc.
Wikimedia Foundation. 2010.
Look at other dictionaries:
climate — /kluy mit/, n. 1. the composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years. 2. a region or… … Universalium
Glossary of fuel cell terms — The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but … Wikipedia
Heating degree day — United States Heating Degree Day map, 1961 1990 … Wikipedia
Earth Sciences — ▪ 2009 Introduction Geology and Geochemistry The theme of the 33rd International Geological Congress, which was held in Norway in August 2008, was “Earth System Science: Foundation for Sustainable Development.” It was attended by nearly… … Universalium
PID controller — A block diagram of a PID controller A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems – a PID is the most commonly used feedback… … Wikipedia
physical science, principles of — Introduction the procedures and concepts employed by those who study the inorganic world. physical science, like all the natural sciences, is concerned with describing and relating to one another those experiences of the surrounding… … Universalium
river — river1 riverless, adj. riverlike, adj. /riv euhr/, n. 1. a natural stream of water of fairly large size flowing in a definite course or channel or series of diverging and converging channels. 2. a similar stream of something other than water: a… … Universalium
photography, technology of — Introduction equipment, techniques, and processes used in the production of photographs. The most widely used photographic process is the black and white negative–positive system (Figure 1 >). In the camera the lens projects an image of… … Universalium
Fuel injection — Fuel rail connected to the injectors that are mounted just above the intake manifold on a four cylinder engine. Fuel injection … Wikipedia
Fuel economy in automobiles — Fuel consumption monitor from a 2006 Honda Airwave … Wikipedia