1、BRITISH STANDARD BS 7074-3: 1989 Application, selection and installation of expansion vessels and ancillary equipment for sealed water systems Part 3: Code of practice for chilled and condenser systems UDC 621.642.3:697.43:621.175:001.4:620.1:006.76(083.75)BS7074-3:1989 This British Standard, having
2、 been prepared under the directionof the Refrigeration, Heating and Air Conditioning Standards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 31 July 1989 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference
3、RHE/7 Draftfor comment 87/73421 DC ISBN 0 580 17147 7 Committees responsible for this BritishStandard The preparation of this British Standard was entrusted by the Refrigeration, Heating and Air Conditioning Standards Policy Committee (RHE/-) to Technical Committee RHE/7, upon which the following bo
4、dies were represented: Associated Offices Technical Committee Association of Consulting Engineers Association of Manufacturers of Domestic Unvented Supply Systems Equipment (MODUSSE) British Marine Equipment Council Building Services Research and Information Association Chartered Institution of Buil
5、ding Services Engineers Heating and Ventilating Contractors Association HEVAC Association Institute of Domestic Heating Engineers Sealed Expansion Vessel Association Waterheater Manufacturers Association Amendments issued since publication Amd. No. Date of issue CommentsBS7074-3:1989 BSI 09-1999 i C
6、ontents Page Committees responsible Inside front cover Foreword ii Section 1. General 1 Scope 1 2 Definitions 1 3 Symbols, designations and units 2 4 Connection of expansion vessel to the system 2 5 Testing and commissioning 3 6 Maintenance 5 7 Workmanship 5 Section 2. Chilled water systems 8 Design
7、 considerations 6 9 Application 6 10 Ancillary equipment 7 Section 3. Condenser water systems 11 Design considerations 12 12 Application 12 13 Ancillary equipment 13 Appendix A Examples of recommended procedure for the calculation of the size of expansion vessels 16 Figure 1 System pressure variatio
8、ns: recommended arrangement 4 Figure 2 System pressure variations: neutral point at pump discharge 4 Figure 3 System pressure variations: neutral point remote from pump 5 Figure 4 Chilled water system 10 Figure 5 Typical expansion percentage of water mixed with anti-freezing agent versus temperature
9、 11 Figure 6 Condenser water (heat reclaim) system 15 Table 1 Symbols, designations and units 2 Table 2 Expansion percentages (e) for various flow temperatures (t f ) from 4 C initial temperature 8 Publications referred to Inside back coverBS7074-3:1989 ii BSI 09-1999 Foreword This British Standard
10、code of practice has been prepared under the direction of the Refrigeration, Heating and Air Conditioning Standards Policy Committee. The code complements BS 4814 and gives recommendations in its three Parts for the installation of expansion vessels in domestic heating and supply systems (Part 1); l
11、ow and medium temperature hot water heating systems (Part 2); chilled water and condenser systems (Part 3); and boosted hot water supply systems. 1) The code deals with the work involved in the general planning, designing and installation of the various systems when the expansion and contraction of
12、the system water is catered for in a sealed diaphragm type vessel. In all other respects the customary design process should be followed for the appropriate system. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible f
13、or their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 18, an inside back cover and a back cover. This standard has been updat
14、ed (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) Planned.BS7074-3:1989 BSI 09-1999 1 Section 1. General 1 Scope This Part of BS 7074 gives recommendations on the application of expansion vessels complying wi
15、th BS 4814 having a maximum pressure of 7 bar 2)for use in the following two types of system. It includes description, design considerations and application. Sections 1 and 2 cover chilled water systems. Sections 1 and 3 cover condenser water systems. NOTE 1Condenser water systems are normally assoc
16、iated with the heat reject side of refrigeration plant. Recommendations are also given on: a) the application and use of ancillary equipment and b) testing, commissioning and maintenance. NOTE 2The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definit
17、ions For the purposes of this Part of BS 7074 the following definitions apply. 2.1 charging pressure the initial pressure to which the gas/air side of the vessel is charged (which is equal to the initial system design pressure) 2.2 closed valve head (P c ) the maximum head developed by a pump under
18、a no-flow condition 2.3 design acceptance factor (a) the ratio of the volume of water due to expansion, to total vessel volume 2.4 diaphragm (or membrane) the flexible means by which the chamber of an expansion vessel is partitioned to maintain separation between the expanding hot water and the gas
19、or air which in consequence becomes compressed. It may be either a literal diaphragm clamped between two parts (or halves) of the vessel, or a bag located by its mouth which is secured to the point of the water connection to the vessel 2.5 expansion percentage (e) the expansion percentage increase i
20、n volume when water is heated to the design ambient temperature 2.6 expansion volume (V a ) the increase in volume of water due to expansion of water when raised to the design ambient temperature 2.7 final system design pressure (P f ) the pressure occurring at the mid-height of the expansion vessel
21、 at the maximum design system temperature 2.8 initial cold water fill temperature (t i ) the basic reference temperature is taken to be 4 C 2.9 initial system design pressure (P i ) the pressure occurring at the mid-height of the expansion vessel at cold fill. This is equal to the static height pres
22、sure plus the pressure margin 2.10 lowest working pressure component (LWPC) the component having the lowest working pressure in the system 2.11 maximum acceptance factor (A) the ratio of maximum acceptance volume of the system to total volume 2.12 maximum acceptance volume (V) the volume of water wh
23、ich the vessel may be allowed to contain 2.13 maximum vessel temperature the maximum water temperature at which the vessel may be allowed to operate continuously 2.14 maximum vessel working pressure the maximum pressure that the vessel may be allowed to contain in operation 2.15 pressure depth (P d
24、) the vertical distance between the component being considered and the mid-height of the expansion vessel situated above it 2.16 pressure margin (P s ) the additional pressure imposed on the circuit to exclude air from the system at the highest point 2) 1 bar = 10 5N/m 2= 100 kPa.BS7074-3:1989 2 BSI
25、 09-1999 2.17 safety valve set pressure (P max ) the pressure at which the safety valve is set for operation 2.18 static height pressure (P h ) the pressure created by the column of water between the uppermost part of the circuit and the mid-height of the expansion vessel 2.19 system flow temperatur
26、e (t f ) the maximum designed temperature of the water circulating in the system 2.20 total system volume (V s ) the total volume of water in the complete system 2.21 total vessel volume (V t ) the volume occupied by gas/air when the vessel is empty of water 3 Symbols, designations and units The sym
27、bols for physical quantities, their designations and units used in this code of practice are given in Table 1. Table 1 Symbols, designations and units 4 Connection of expansion vessel to the system 4.1 General The neutral point of the system is the point of connection of the pipework to the expansio
28、n vessel. It is recommended that the expansion vessel is in the system return pipework close to the heat exchanger. The filling position should be into the expansion pipework. The point of connection of the expansion vessel(s) into the system having been clearly defined, the physical location of the
29、 vessel can be anywhere. 4.2 Location of pump relative to expansion vessel 4.2.1 General. When the pump in the system is not operating the only pressure existing varies between P iand P fdepending upon the water temperature. When the pump is started the pressure within the system will change from it
30、s original static pressure conditions to a completely new set of pressure conditions. This new pressure condition is defined as the pump head and is indicated by the pressure drop between the suction and discharge of the pump. The pressure at the pump discharge will be higher than the system pressur
31、e at the pump suction by an amount equal to the pump head. The pressure drop due to friction within the system will gradually decrease the system pressure from that existing at the pump discharge to the lower pressure existing at the pump suction. With the pump running, the system pressure will chan
32、ge generally as illustrated in Figure 1, Figure 2 and Figure 3. Attention is drawn to the point of no pressure change being relative to the point of connection of the expansion vessel into the system. The pump only has the ability to create the pressure difference across itself and therefore there i
33、s no reason why the full pump head should not appear on the suction side of the pump as shown in Figure 2. It will be noted that the position of no pressure change (the neutral point) is different from that shown in Figure 1. By dictating the point of no pressure change (the neutral point), system p
34、ressure changes by pump operation can be controlled. In Figure 3, where the neutral point has been changed once again, a new set of pressure characteristics pertain. Symbol Designation Unit A Maximum acceptance factor a Design acceptance factor e Expansion percentage P c Closed valve head bar gauge
35、P d Pressure depth bar gauge P f Final system design pressure bar gauge P h Static height pressure bar gauge P i Initial system design pressure bar gauge P max Safety valve, set pressure bar gauge P s Pressure margin bar gauge t a Maximum ambient temperature C t f System flow temperature C t i Initi
36、al cold water fill temperature C V Maximum acceptance volume L V a Expansion volume L V s Total system volume L V t Total vessel volume LBS7074-3:1989 BSI 09-1999 3 4.2.2 Neutral point. The point of no pressure change, or the neutral point, is the point where the expansion vessel is connected to the
37、 system. This is because the air gas cushion in the expansion vessel follows basic gas laws and the change in gas pressure has to be accompanied by a change in gas volume. A change in gas volume in the vessel has to be accompanied by a change of water volume in the vessel. It follows that a change i
38、n water volume in the vessel has to be accompanied by a change of water volume in the system; since water is incompressible, pump operation cannot increase or decrease the system water volume therefore pump operation cannot change vessel pressure. Since vessel pressure cannot change due to pump oper
39、ation, the junction of the expansion vessel with the system has to be a point of no pressure change regardless of whether or not the pump operates. 4.2.3 Neutral point at pump suction. Figure 1 illustrates a system in which the neutral point is located at the pump suction. The pressure changes cause
40、d by pump operation are therefore added to the original system static pressure. Because all system pressure changes are additive and positive there is no possibility of pump cavitation or air being drawn into the system. 4.2.4 Neutral point at pump discharge. Figure 2 shows a system where the point
41、of no pressure change is located at the pump discharge. All pressure changes caused by pump operation are subtracted from the original pressure and are of a negative type; under certain conditions this can cause unsatisfactory results. If the pressure decrease below the original static pressure is g
42、reat enough, the system pressure could drop, circulation will be unstable and pump cavitation can occur with a resultant pump failure. If the pressure drops below atmospheric pressure, air can be sucked in at the vent, air pockets are created and circulation blocked, it is strongly recommended there
43、fore that the neutral point should not be located at the pump discharge. 4.2.5 Neutral point remote from pump. By locating the expansion vessel at some distance from the pump, the system pressure change due to pump operation would appear as shown in Figure 3. The expansion vessel junction would be t
44、he neutral point and all pressure system changes would be referred from that point. Pressure gauge readings at the pump suction and discharge would show partially positive and partially negative readings with reference to the original non-operating static pressure condition. The pressure changes wou
45、ld be a function of the system pipe friction pressure drop between the pump and the vessel. It is emphasized that the problems created in systems where the neutral point is such that the pump head is all under suction (see Figure 2) are more likely to occur in higher head pump systems. Therefore in
46、dealing with microbore systems it is important that the relative position of the neutral point and pump be fully understood in order that the most satisfactory system operation can be effected. 4.2.6 Recommended arrangement. If the expansion vessel is placed at the suction side of the pump, the pump
47、 suction pressure will not change regardless of whether or not the pump is operated; because the pump suction cannot change, the pump discharge pressure has to change. The pump differential head is then manifested as a positive increase in pressure at the pump discharge as shown in Figure 1. The pre
48、ssure increase due to pump head will then decrease around the system, depending upon the various friction losses in the system until at the pump suction the original static pressure is obtained. Because the pump suction pressure is unchanged due to pump operation it is suggested that the chiller be
49、placed at the pump suction; this is the recommended relative arrangement of pump, chiller and expansion vessel within a system. 5 Testing and commissioning 5.1 Pressure testing the system Expansion vessels, pressure switches, safety valve(s) and fill unit have to be isolated prior to hydraulic pressure testing. This is to ensure that these components are not damaged by over pressurization.BS7074-3:1989 4 BSI 09-1999 Figure 1 System pressure variations: recommended arrangement Figure 2 System pressure variations: neutral point at pump dis
