YORK_HVAC European catalogue_Mar. 2021_EN | Page 109

Minimum system water volume

To allow the Chiller or Heat Pump to operate smoothly at low load capacities sufficient thermal storage is required in the primary water circuit to give at least 5 minutes operation when the machine is not running . This will ensure that the equipment will not continuously stop and start at low load conditions and consequantly cause undue wear on the compressor . The following formula will satisfy the toral required thermal storage volume :

V =

( N x 60 x Z ) 4.18 x dt

V = Total system water content ( Litres )( 4.18 x dt ) N = Capacity of the Chillers first capacity step ( kW )( 4.18 x dt ) Z = Minimum allowable running time ( minimum 5 min .) dt = Temp . difference at the minimum partload condition

V = 35.88 x S x Q S = Minimum capacity step ( at lowest operating ambient ) Q = Full capacity at nominal conditions

Warm water system

The leaving water temperature from a Heat Recovery Chiller or a Heat Pump is normally between 45 ° C and 60 ° C depending on the refrigerant that the machine is charged with . For Heat Pumps more heating capacity and higher operating efficiency is available with lower leaving water temperatures . Water temperatures of 45 ° C to 50 ° C are quite adequate for the selection of heating coils in Air Handling Units and Fan Coils . Refrigerant to water condensers are limited in the volume of water that can be passed through them and it is necessary that this limitation is considered during the system design process . This may result in a larger water temperature differences than those used in a normal Boiler fed low temperature hot water system . The water temperature can be increased from a Boiler but measures must be taken to ensure that the return water to the Chiller or Heat pump cannot ever exceed 60 ° C .

Chiller condenser connection

In order to ensure a trouble-free operation of the cooling water pump during startup of the system , the entire cooling water piping should be as far as possible below the operating level of an open circuit cooling tower . This prevents emptying of the cooling water lines in the cooling tower trough . If multiple cooling towers are used in a common cooling water circuit , compensation pipes must be installed between the cooling tower tanks in order to keep the cooling water in all cooling towers at the same level . If more than one water entry into the cooling tower is required , install throttle valves to balance the flow between circuits . Check that the pressure of the spray nozzles and the pressure of the make-up water are not exceeded .

Chiller condenser water systems

To ensure satisfactory pump operation at start-up and to prevent overflowing of the Cooling Tower sump all condenser piping , and as much tower piping as possible , should be installed below the operating level of the tower . If multiple towers are used on a common system equalising lines should be installed between the sumps of the separate Cooling Towers to ensure balanced water level in all the towers . If more than one inlet connection is required to a tower balancing valves should be installed to give the required flow to each circuit . Check that the maximum spray water and make-up water pressures are not exceeded .

YORK Air-Conditioning Products 109