Refrigeration, air-conditioning and cooling technology - 2007.pdf

More documents

Recommendations

Info

PLH_KKK_32_85.QXP 25.05.2007 10:10 Uhr Seite 32
PLH_KKK_32_85.QXP 25.05.2007 10:10 Uhr Seite 33Pump performance controlThe volume flow conveyed through a circulatingpump is dependent on the thermal output/coolingoutput requirement of the system beingsupplied. This requirement fluctuates dependingon the following factors:• Climatic changes• User behaviour• Extraneous heat influence• Influence of hydraulic control devices, etc.The circulating pump designed for maximumload status is adapted by means of a continuoussetpoint/actual-value comparison to the relevantsystem operating state. This automaticcontrol serves to adapt the pump performanceand thus also the power consumption continuouslyto the actual requirement/demand.Electronically controlled pumps from Wilo areable to control the mass flow automatically.This can help avoid throttling and makes anadjustment to the system duty point possible.In addition to the reduced power consumptionof the pump, throttling elements can also bedone without. This way, additional installationand material costs can be noticeably reduced.The same result can be achieved with Wilo controldevices which aren't directly mounted onthe pump.Control mode ∆p-cIn the ∆p-c control mode, the electronics circuitrymaintains the differential pressure generatedby the pump constant at the setpoint valueH S over the permitted volume flow range.Delivery head H [m]∆p-c controln maxn regelH SetpointH Setpoint-min∆p-cFlow Q [m³/h]I. e., any reduction of flow volume (Q) due tothrottling of the hydraulic regulating deviceswill in turn decrease the pump performance tomatch actual system demand by reducing thespeed of the pump. In parallel with speed alteration,the power consumption is reduced to below50 % of the nominal power. The applicationof differential-pressure control requires a variableflow volume in the system. Peak-load operation,e.g. in conjunction with a twin-headpump, will be effected automatically and loadsensitively.If the capacity of the controlledbase-load pump becomes insufficient to coverthe increasing load demand the second pumpwill automatically be started to operate in parallelto cover the risen demand. The variable speedpump will then be run down until reaching thepreset differential-pressure setpoint value.It is generally recommended to pick off the differential-pressuredirectly at the pump and tomaintain it there at a constant level. An alternativewould be to install the signal transmitter inthe system – as a remote signal transmitter inthe so-called index circuit of the system (controlrangeextension). Operation with a remote signaltransmitter will partly allow much larger speed reductionsand thus pump performance reductions.It is essential in this respect that the selectedmeasuring point is valid for the consumptionperformance of all the system sections. Wherethis calculated measuring point in the index circuitmay be subject to shifting to other parts ofthe pipe system, optimisation by means of theWilo DDG impulse selector is preferable. Measuringpoints ranging from 2 to 4 can be comparedon a continuous basis. Only the lowestmeasured value forms the basis for the setpoint/actualvalue comparison by the CR controller.Delivery head H [m]Control curve for remote signal transmittersPump curveSystem curve for themeasuring pointIntersectionpoint =duty pointFlow Q [m³/h]Wilo Planning Guide - Refrigeration, air-conditioning and cooling technology 02/2007 33
Page 1 and 2: PLH_Titel_KKK.qxd 25.05.2007 10:21
Page 3 and 4: PLH_KKK_U2_31.QXP 25.05.2007 11:01
Page 31: PLH_KKK_U2_31.QXP 25.05.2007 11:02
Page 35 and 36: PLH_KKK_32_85.QXP 25.05.2007 10:10
Page 83 and 84:
PLH_KKK_32_85.QXP 25.05.2007 10:11
Page 85 and 86:
PLH_KKK_32_85.QXP 25.05.2007 10:11
Page 87 and 88:
PLH_KKK_86_103.QXP 25.05.2007 10:24
Page 89 and 90:
PLH_KKK_86_103.QXP 25.05.2007 10:24
Page 91 and 92:
PLH_KKK_86_103.QXP 25.05.2007 10:24
Page 93 and 94:
PLH_KKK_86_103.QXP 25.05.2007 10:24
Page 95 and 96:
PLH_KKK_86_103.QXP 25.05.2007 10:28
Page 97 and 98:
PLH_KKK_86_103.QXP 25.05.2007 10:28
Page 99 and 100:
PLH_KKK_86_103.QXP 25.05.2007 10:35
Page 101 and 102:
PLH_KKK_86_103.QXP 25.05.2007 10:42
Page 103 and 104:
PLH_KKK_86_103.QXP 25.05.2007 10:42
show all

Refrigeration, air-conditioning and cooling technology - 2007.pdf

Create successful ePaper yourself

Delete template?

Save as template?