Dimplex Unvented Water Heater installation manual External Expansion Vessel Optional

Dimp-15278-SCx_Instructions 31/3/06 9:32 am Page 9

TUNDISH

The tundish supplied must be fitted visible to the occupier. The discharge pipe must be 22mm copper pipe. Regulations do not permit more than 3 x 90-degree bends between the SCx unit and the outflow. Between the temperature & pressure relief valve and the first 90-degree bend there must be a fall of at least 300mm. The fall of the pipework must be continuous and the pipe should terminate in the gully or be bent backwards onto an outside wall, in a place where discharge cannot be injurious to persons.

If you need to site the SCx unit In the middle of the house your discharge pipe to the tundish can be as far away as 9m, which in most cases is enough to run the final discharge point. After 9m, increase the pipe size to a greater diameter than 22mm and accordingly for subsequent 9m lengths, see table 1 on page 10.

COMMISSIONING THE SCx UNIT

Switch on electricity to the immersion heater(s) (Direct system) or switch on the boiler (Indirect system). Refer to the boiler manufacturers instructions on commissioning.

Bring the unit to its maximum temperature setting of approx. 60 degrees Celsius. You should, on operating the water taps, have a good flow of hot and cold water assuming adequate water is supplied to the SCx unit.

Check the water does not discharge via the tundish pipework during heating.

Recheck all fittings/joints for possible leaks.

On completion of the installation, before turning on the mains water supply ensure that all residual materials are removed by means of flushing the system with a suitable cleaner.

EXTERNAL EXPANSION VESSEL – OPTIONAL

This smaller tank is connected to the cold-water inlet side of the vessel. Mount the tank according to separate manufacturers instructions provided with the External Expansion vessel.

See fig 1 page 5.

SCALE

In hard water areas lower water temperatures can result in less scale being deposited.

If water softener is used it should be capable of flows of approx. 50 lt/min, this will maintain maximum performance of the SCx unit.

If no descaler or softener is used then the heating element(s) will need descaling periodically for maximum efficiency.

DRAINING

Switch off electrical power to immersion heaters and/or shut down the boiler. Close the stopcock valve to isolate the SCx unit.

Attach hosepipe to the drain cock having sufficient length to take water to a suitable discharge point.

Open drain cock

Open hot water tap nearest SCx unit.

If water fails to drain from SCx unit, vent the system by opening the temperature pressure relief valve.

SCHEMATIC DISCHARGE

PIPE ARRANGEMENT

Fig.6

DISCHARGE PIPEWORK

It is a requirement of Building Regulations that any discharge from an unvented system is conveyed to where it is visible, but will not cause danger to persons in or about the building. The tundish and discharge pipes should be fitted in accordance with the requirements and guidance notes of Building Regulations. Building Regulation G3 Requirements and guidance section 3.9 reproduced in the following sections.

Information Sheet No. 33 available from the British Board of Agreement gives further advice on discharge pipe installation.

G3 REQUIREMENT

‘…there shall be precautions…to ensure that the hot water discharged from safety devices is safely conveyed to where it is visible but will not cause danger to persons in or about the building.’

G3 GUIDANCE SECTION 3.9

The discharge pipe (D1) from the vessel up to and including tundish is generally supplied by the manufacturer of the hot water storage system. Where otherwise the installation should include the discharge pipe (s) (D1) from the safety device(s). In either case the tundish should be vertical located in the same space as the unvented hot water storage system and be fitted as close as possible and within 500mm of the safety device e.g the temperature relief valve.

The discharge pipe (D2) from the tundish should terminate in a safe place where there is no risk to persons in the vicinity of the discharge, preferably be of metal and:

a.be at least one pipe size larger than the nominal outlet size of the safety device unless it’s total equivalent hydraulic resistance exceeds that of a straight pipe 9m long ie. discharge pipes between 9m and 18m equivalent resistance length should be at least two sizes larger, than the nominal outlet size of the safety device between 18 and 27m, at least 3 sizes larger and so on. Bends must be taken into account in calculating flow resistance. Refer to Table 1 overleaf and fig. 6.

An alternative approach to sizing discharge pipes would be to follow BS 6700:1987 specification for design installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages, Appendix E, section E2 and table 21.

b.have a vertical section of pipe at least 300mm long, below the tundish before any elbow or bends in the pipework.

c.be installed with a continuous fall.

d.have discharges visible at both the tundish and the final point of discharge but where this is not possible or is practically difficult there should be clear visibility at one or other of these locations.

Examples of acceptable discharge arrangements are:

i)ideally below a fixed grating and above the water seal in a trapped gully.

ii)downward discharges at low level; i.e. up to 100mm above the external surfaces such as car parks, hard

standings, grassed areas etc. are acceptable providing that where children may play or otherwise come into contact with discharges a wire cage or similar guard is positioned to prevent contact, whilst maintaining visibility.

iii)discharges at high level; e.g into a metal hopper and metal down pipe with the end of the discharge pipe clearly visible (tundish visible or not) or onto a roof capable of withstanding high temperature discharges of water and 3m from any plastics guttering system that would collect such discharges (tundish visible.)

iv)where a single pipe serves a number of discharges, such as in blocks of flats, the number served should be limited to not more than 6 systems so that any installation discharging can be traced reasonably easily. The single common discharge pipe should be at least one pipe size larger than the largest individual discharge pipe (D2) to be connected. If unvented hot water storage systems are installed where discharges from safety devices may not be apparent i.e. in dwellings occupied by blind, infirm or disabled people, consideration should be given to the installation of an electronically operated device to warn when discharge takes place.

Note: The discharge will consist of scalding water and steam. Asphalt, roofing felt and non-metallic rainwater goods may be damaged by such discharges.

WORKED EXAMPLE OF DISCHARGE PIPE SIZING

The example below is for a G1/2 temperature relief valve with

a discharge pipe (D2) having 4 No elbows and length of 7m

from the tundish to the point of discharge.

From table 1: (overleaf)

Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from G1/2 temperature relief valve is 9.0m

Subtract the resistance for 4 No 22mm elbows at 0.8m each = 3.2m

Therefore the permitted length equates to 5.8m

5.8m is less than the actual length of 7m therefore calculate the next largest size.

Maximum resistance allowed for a straight length of 28mm pipe (D2) from a G1/2 temperature relief valve equates to 18m

Subtract the resistance of 4 No 28mm elbows at 1.0m each = 4.0m

Therefore the maximum permitted length equates to 14m

As the actual length is 7m a 28mm (D2) copper pipe will be satisfactory.

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