Baxi Potterton BBU 15 HE manual Sealed Systems

		Temporary
		Hose
Mains Water	Hose	Stop
Supply	Union
		Valve
(Service Pipe)
		Double
		Check
		Valve
		Heating
		System

4.0System Details

4.7Sealed Systems (cont)

4.Expansion Vessel. A diaphragm type expansion vessel to BS 4814:1 shall be fitted close to the inlet side of the pump. The connecting pipework should not be less than 15mm.

Pipework connecting the expansion vessel should not incorporate valves of any sort.

Methods of supporting the vessel are supplied by the vessel manufacturer.

The nitrogen or air charge pressure of the expansion vessel shall not be less than the hydrostatic head, (height of the top point of the system above the expansion vessel). To size the expansion vessel it is first necessary to calculate the volume of water in the system in litres. The following volumes may be used as a conservative guide to calculating the system volume.

Filling a Sealed Water System (Method 1)

Mains Topping Up Method

NOTE: This method of filling a sealed system may only be used if acceptable to Local Water Undertaking

Mains Water

Supply

Cistern

Filling a Sealed Water System (Method 2)

Cistern Filling Method

NOTE: Cistern to be supplied through a temporary connection from a service pipe or cold water distributing pipe

Fig. 7

Pressure Pump Reducing Valve (if required)

Stop

Valve

Heating

System

Fig. 8

Boiler Heat Exchanger:	1.55 litres
Small Bore Pipework:	1 litre per kW of system output
Micro Bore Pipework:	7 litre
Steel Panel Radiators:	8 litre per kW of system output
Low Water Capacity Radiators:	1 litre per kW of system output
Hot Water Cylinder:	1 litre per kW of system output

If the system is extended, the expansion vessel volume may have to be increased unless provision has been made for extension. Where a vessel of the calculated size is not available, the next available larger size should be used.

The boiler flow temperature is controlled at approx. 75°C.

The vessel size can now be determined from the information in table 1 where V = System volume in litres.

5.Cylinder. The hot water cylinder must be an indirect coiler type.

6.Method of Make Up. Provision shall be made for replacing water loss from the system either:-

a)From a make up vessel or tank mounted in a position higher than the top point of the system and connected through a non-return valve to the system on the return side of the hot water cylinder or the return side of all heat emitters.

or

b)Where access to a make up vessel would be difficult by using the mains top up method or a remote automatic pressurisation and make up unit.

7.Mains Connection. There shall be no connection to the mains water supply or to the water storage tank which supplies domestic hot water even through a non-return valve, without the approval of the Local Water Authority.

8.Filling Point. A filling point connection on the central heating return pipework must be provided to facilitate initial filling and pressurising and also any subsequent water loss replacement/refilling.

The sealed primary circuits may be filled or replenished by means of a temporary connection between the circuit and a supply pipe, provided a ‘Listed’ double check valve or some other no less effective backflow prevention device is permanently connected at the inlet to the circuit and the temporary connection is removed after use.

Vessel Charge Pressure (bar)	0.5	1.5
Initial System Pressure (bar)	1.0	1.0
Expansion Vessel Volume (litres)	V x 0.11	V x 0.087

Table 1

The filling method adopted must be in accordance with all relevant water supply regulations and use approved equipment.

Your attention is drawn to: for GB: Guidance G24.2 and recommendation R24.2 of the Water Regulations Guide. for IE: the current edition of IS 813 “Domestic Gas Installations”.

14© Baxi Heating UK Ltd 2009