Unvented Hot Water Infographics

Direct - Unvented hot water installation with an Inlet control group (combination valve)

The combination valve controls the water into the cylinder and features four valves within it. They are as follows;

• In line strainer

• Pressure reducing valve

• Single check valve

• Expansion/pressure relief

The source of heat on this image is an Immersion heater of 3kW and it has no secondary return on the image. 

Indirect - Unvented hot water installation with an Inlet control group (combination valve)

The source of heat in this image is the boiler (system) which supplies the heat for the hot water and the heating. It has two heating zones which are controlled by the motorised zone valves on the primary flow from the boiler, one to the hot water storage vessel and the other to the heating circuit. In this case to some heat emitters (radiators).

Electrical wiring diagram for the Image above

Valves in series (no inlet control group)

In some cases you may be asked to install an Unvented cylinder without an inlet control group (combination valve). This is commonly known as valves in series. The valves that are within the combination valve are installed individually in order as can be seen below.

D1 & D2 - Discharge pipes

Worked example- 

The example below is for a G½ temperature relief valve with a discharge pipe (D2) having 4 No. 22mm elbows and length of 7m from the tundish to the point of discharge. 

From Table 3.1: Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from a G½ temperature relief valve is: 9.0m Subtract the resistance for 4 No. 22mm elbows at 0.8m each = 3.2m.

Therefore the maximum permitted length equates to 5.8m which, is less than the actual length of 7m therefore calculate the next largest size. 

See below image for the calculation when you have to increase the diameter of the D2 pipework.

Commissioning

The most important thing to consider when commissioning systems/appliances/components is always follow the manufacturers instructions/literature. They will guide you through the correct procedures and the expected outcomes. 

FILLING 

First you must ensure that the pressure in the expansion vessel is the same as the setting of the pressure reducing valve i.e. 3 bar. The valve is of the Schrader car tyre type. Check all the connections for water tightness including any factory made connections such as the immersion heater and the temperature and pressure relief valve. Prior to filling, open the hot tap furthest away from the cylinder to expel air. Open the cold main isolation valve and allow the unit to fill. 

Walk the installation, visually check that the outlets are closed for example any drain offs, check all joints are tight and soldered etc. 

Once the cylinder has been fully commissioned it should be heated to its normal operating temperature. Draw off secondary hot water to each outlet and allow hot water to flow from each outlet for at least 30 seconds to remove any flux residue from the pipe work within the secondary hot water system. Then fully drain the cylinder and re-fill to ensure that all flux residues is removed from the system. 

INDIRECT UNITS 

Fill the primary circuit according to the boiler manufacturers’ commissioning instructions. Any additives used in the heating system water circulating through the cylinder coil must be compatible for use with stainless steel cylinders. Ensure the lever on the two port valve is set to the filling position. When full, move the lever back. Switch the programmer to Domestic Hot Water (DHW) and allow the unit to start to heat. Adjust the dial of the dual thermostat to between 30°C and 70°C as required.

STORAGE TEMPERATURE 

60-65°C is the recommended storage temperature for both direct and indirect cylinders. In hard water areas consideration should be given to reducing this to 50-55°C. In many healthcare applications the guidance on Legionella control and safe water delivery temperatures will require storing the water at 60-65°C, distributing at 50- 55°C and using thermostatic mixing valves to control the final temperature. For details consult the NHS Estates Guidance on safe hot water temperatures.

TECHNICAL DATA

When the system is full, check with a weir cup the flow rate at each outlet (tap) record the information in litres per minute. Check the waste pipe at this point too as the water is being discharged into the appliances (sinks, basins, baths). 

Make sure all of the readings are still suitable for the installation/property and meet the requirements of either the homeowner/new appliance via the manufacturer's instructions that will tell you how the appliance has been designed to function with pressure and flow rates.

Completing paperwork-

You may need to complete commissioning paperwork such as a benchmark sheet or some other form of record. At this point you will need the pressures that you have recorded and the flow rates. 

If you are working on a hot and cold water system/installation then some temperature readings will also be required to be recorded on the form. 

For example- 

Cold water flow rate 9 l/m - Temperature 12 degrees C

Hot water flow rate 8 l/m - Temperature 48 degrees C

Temperature difference 36 degrees C

Check the temperature rise is in accordance with the manufacturer's literature if on a combination boiler for example.

Commissioning Checklist

Trouble Shooting

Servicing

A guide from the Hot Water Association 2018