1、BRITISH STANDARD BS 4857-1: 1972 Methods for Testing and rating terminal reheat units for air distribution systems Part 1: Thermal and aerodynamic performance UDC 697.978:697.356.001.42BS4857-1:1972 This British Standard, having been approved by the Refrigeration, Heating and Air Conditioning Indust
2、ry StandardsCommittee, was published under the authority ofthe Executive Board on 11 October 1972 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference RHE/6 Draft for comment 71/30799 ISBN 0 580 07323 8 Co-operating organizations The Refrigeration, Heatin
3、g and Air Conditioning Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Association of Consulting Engineers* Association of Manufacturers of Dom
4、estic Electrical Appliances Boiler and Radiator Manufacturers Association* British Mechanical Engineering Confederation British Oil and Gas Firing Equipment Manufacturers Association British Refrigeration and Air Conditioning Association* Department of Health and Social Security* Department of the E
5、nvironment Electricity Council, The Central Electricity Generating Board and the Area Boards in England and Wales Engineering Equipment Users Association Gas Council Heating and Ventilating Contractors Association* Heating and Ventilating Research Association* HEVAC Association* Institute of Fuel In
6、stitute of Refrigeration* Institution of Electrical Engineers Institution of Gas Engineers Institution of Heating and Ventilating Engineers* Lloyds Register of Shipping Ministry of Defence, Navy Department* National Coal Board Royal Institute of British Architects Water-tube Boilermakers Association
7、 The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Department of the Environment, Building Research Station
8、 Greater London Council Oil Appliances Manufacturers Association Steel Radiators b) a constant flow rate controller; c) a sound attenuator. the casing is so designed that the whole of the air discharged from the device is obtained from the inlet duct NOTEWhen the device contains a constant flow rate
9、 controller, it is normally referred to as a single duct terminal reheat box. When the device contains a manual damper, it is normally referred to as a terminal reheat unit. 2.2 flow rate controller a device mounted within the casing for the purpose of maintaining a constant air-flow rate through th
10、e casing when the pressure differential between high and low pressure sides varies within the limits for which the equipment is designed NOTEA flow rate controller normally maintains a constant air-flow rate to within 5% of the maximum air-flow rate of the device, within the pressure differential ra
11、nge of about200N/m 2(2mbar) to1500N/m 2(15mbar). there are different types of flow rate controllers, such as: a) Mechanical constant flow rate controller. Self-actuating. This type derives its power from the air stream and not from any external source. b) Mechanical variable flow rate controller. As
12、 fora) above, but with its flow rate varied by an external signal. c) Pneumatic, electric, etc., flow rate controllers. Controllers deriving their power from an external source. They can be either of the constant or variable type. 3 Nomenclature Symbol Definition Units A i Area of air inlet duct m 2
13、 A t Area of water supply tube m 2 c p Specific heat capacity kJ/kg C H D Hydraulic diameter (= 4 area/perimeter) m K w Temperature correction factor m Water mass flow rate kg/s p Pressure relative to atmosphere N/m 2 p Pressure drop N/m 2 p c Hydraulic pressure drop at 80 C N/m 2 p m Measured hydra
14、ulic pressure drop corrected for height difference N/m 2 p b Atmospheric pressure bar Q Heat transferred kWBS4857-1:1972 2 BSI 11-1999 Suffixes 4 Instrumentation 4.1 Temperature 4.1.1 The measurement of temperature shall be by means of mercury-in-glass thermometers, resistance thermometers or the th
15、ermocouple and potentiometer. Temperature measuring instruments shall comply with the requirements of BS1041. 4.1.2 The water temperature at entry and exit shall be measured by means of instruments inserted in oil-filled pockets similar to those shown inFigure 1. If mercury-in-glass thermometers are
16、 used they shall comply with the requirements of BS593 partial immersion ranges, and shall be graduated in intervals not exceeding0.1 C. 4.1.3 All temperature measuring instruments shall be calibrated to an accuracy of0.1 C. 4.2 Water flow measurement 4.2.1 The measurement of water flow shall prefer
17、ably be by means of direct weighing (for water temperatures above90 C it would be advantageous to use one of the methods described in BS1042 Part1). The water leaving the test rig shall be collected in vessels of known weight, and weighed on a beam-type weighing machine, having an accuracy of0.1% ov
18、er the range of weight used in the test. The weight of each vessel used shall not exceed50% of the weight of its normal contents. Means shall be taken to minimize evaporation from the vessels awaiting weighing. The net weight of each charge shall be recorded by weighing the vessel both after emptyin
19、g the previous charge and after filling. 4.2.2 The above method is suitable for water exit temperatures up to about90 C using the arrangement of equipment shown inFigure 2. For higher water exit temperatures it may be necessary to cool the water leaving the unit before it is discharged into the meas
20、uring vessel. Care shall be taken to check any after-cooler for leaks. 4.2.3 An alternative to the method of direct weighing described in4.2.1 is shown inFigure 3, together with a suitable water supply system for water temperatures above90 C. 4.3 Air flow measurement Air flow measurement shall compl
21、y with the requirements of BS1042-1 or alternatively, a flow meter may be calibrated in situ using the methods given in BS1042-2 2) . Symbol Definition Units Density kg/m 3 t Temperature C U Air velocity m/s V Air volume flow rate m 3 /s a inlet air i inlet water o outlet water f flow meter r refere
22、nce air s static pressure w water Reference conditions for air: Temperature 20 C Pressure 1013.25 mbar (101.325kN/m 2 ) Density 1.2 kg/m 3 Relative humidity 43%BS4857-1:1972 BSI 11-1999 3 4.4 Manometers 4.4.1 The minimum differential pressure measurement for air flow measurement shall be25N/m 2for i
23、nclined U-tube manometers and micromanometers and500N/m 2for vertical U-tube manometers. 4.4.2 All manometers shall be calibrated against an accepted standard. 4.4.3 It shall be possible to read all manometers to1% of the indicated reading. 5 Test for casing leakage This test shall be carried out in
24、 accordance with BS 2) . In the case of units fitted with a flow control device, leakage tests shall be carried out with this device in the open position. 6 Test of constant flow rate controller characteristics Units fitted with a constant flow rate controller shall be tested for the performance of
25、the constant flow rate controller by the method described in BS 2) . 7 Test for air flow pressure characteristics Units fitted with a manual or remote controlled air flow damper shall be tested for the relationship between the inlet total pressure and air volume flow rate, with the damper set in the
26、 fully open position. 7.1 An air inlet duct of internal dimensions equal to the nominal dimensions of the inlet of the unit under test, and of a minimum straight length5 hydraulic diameters, shall be fitted to the unit inlet. A ring of four wall static taps (constructed to BS1042-2 2) ) shall be fit
27、ted at a point1 inlet duct hydraulic diameters from the unit inlet; a flow straightener shall be fitted4 hydraulic diameters and a wire screen3 hydraulic diameters upstream from the static taps. The unit and duct assembly shall be connected to an air flow meter, fan and flow control system as shown
28、inFigure 4. 7.2 The inlet air temperature shall be measured at a point, hydraulic diameter downstream of the static taps, at the four stations indicated in the inset diagram inFigure 4. The inlet air temperature (t a ) shall be the mean of these four measurements. 7.3 The desired air flow shall be s
29、et and when steady state conditions have been achieved measurements of the following shall be recorded. NOTEFor the purposes of this test steady state conditions are said to exist when the inlet air temperature has not varied by more than0.25 C and the flow meter pressure drop and static pressure at
30、 the unit inlet have not varied by more than2% over a period of5min. 2) BS . . . . “Testing and rating of air control devices for air distribution systems”, Part1, “Aerodynamic testing of constant flow rate assemblies without a heat exchanger”. (In course of preparation.) p f flow meter pressure dro
31、p (N/m 2 ) static pressure upstream of the flow meter (N/m 2 ) t f the temperature at the flow meter ( C) p s the unit inlet static pressure (N/m 2 ) t a the unit inlet temperature (mean of four) ( C) and p b the atmospheric pressure (bar). The air volume flow rate at the flow meter (V f ) is calcul
32、ated from p f , p s , t f , and p b . The mean velocity at the unit inlet (U i ), is calculated from the following equation. where A iis the area of the inlet duct (m 2 ) fis the density of air at the flow meter (kg/m 3 ) iis the density of air at the unit inlet (kg/m 3 ). ps f U i V f A i - f i - =
33、BS4857-1:1972 4 BSI 11-1999 7.4 The test described above shall be repeated at four other air flow rates spread evenly through the flow range of the unit, covering this range to within20% at each end. The total pressure ( T ) shall be plotted against the flow rate converted to reference conditions (V
34、 r = V f f / r ), on logarithmic graph paper, and the best straight line drawn through the experimental points. This line shall be used for the determination of the total pressure loss of the unit with the inlet damper fully open. 8 Heat transfer measurements The test apparatus and measurements desc
35、ribed in this clause will enable the performance of the unit to be determined at any air and water flow rate and temperature within and to10% outside of the range of test measurements. The error involved in the interpolations and extrapolations should not exceed5%. Two test methods are described, on
36、e for a limited temperature range and one for a wide temperature range. 8.1 Heat transfer apparatus 8.1.1 There shall be available a means for providing and controlling a continuous supply of hot water at any temperature and flow rate that may be required for the test. 8.1.2 Typical arrangements of
37、the apparatus are shown inFigure 2 and Figure 3. 8.1.3 The pipework shall be arranged to give an unobstructed straight run at entry to and exit from the unit under test, the pipe diameter being equal to that demanded by the unit connections and of length equal to five pipe diameters. 8.1.4 Hydraulic
38、 resistance side wall tappings shall be fitted adjacent to the connections to the unit. These tappings shall be as specified inFigure 5a and connected to form a piezometric ring. The hydraulic pressure drop shall be measured by means of an inverted U-tube manometer similar to that shown inFigure 5b.
39、 8.1.5 The lengths of pipe between the temperature measurement positions, the unit connections and the unit casing shall be insulated with at least40mm thickness of insulating material having a thermal conductivity not exceeding0.06W/m C. 8.1.6 The air supply system described in7 shall be connected
40、to the unit air inlet, and an outlet duct(s) of internal dimensions equal to those of unit outlet(s) and of length equal to at least2outlet hydraulic diameters fitted to the unit outlet(s). 8.2 General test instructions 8.2.1 The inlet air temperature shall be in the range from15 C to25 C and shall
41、not differ from the temperature in the space surrounding the unit under test by more than2 C. 8.2.2 Before commencing the test the following shall be carried out: 1) bleed the water system to remove all air; 2) start the air supply system and set to the desired flow rate; 3) circulate the water thro
42、ugh the coil and regulate the flow and temperature to those desired for the test; 4) record the barometric pressure. 8.2.3 The test shall be carried out under steady state conditions, and these shall be said to exist when the following measurements do not vary over a period of30min by more than the
43、specified amount from their mean value. The mean inlet total pressure (p T ) at reference conditions is calculated from the following equation where ris the reference density of air =1.2kg/m 3 . Inlet air temperature (t a ) 1.0 C Inlet water temperature (t i ) 1.0 C Water flow rate (m) 2% Air flow rate (V) 2%
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