Anti-Scald Valve

Best practice calls for the fitting of a thermal mixing (anti-scald) valve. This applies to all hot water systems and not just solar heated water systems. Many solar systems in Ireland are installed with a large collector area and will heat the cylinder to high temperatures during good weather. It is imperative to reduce the risk of sclading at taps that a good quality anti scald valve is installed. In addition storing water above 60°C will legionella bacteria so is becoming more of a consideration to install thermal mixing valves. The ideal maximum, safe temperature for hot tap water is 50 C.

The maximum bathing temperature recommended for young children is 38 C.

Minimising flow problems when installing Anti scald valves.

A 3/4" Mixing valve will typically have a KVS of 1.5. Using a 2 meter head (20 kPa) the valve will allow about 13 litres/minute flow. A typically 1" mixing valve has a KVs of 3.0, using the chart above, a 2 meter head drop, the valve will allow approx 22 litres/flow. Experience has shown that a vented cylinder fed from a low attic tank can experience flow problems in showers unless a 1" valve is used.

Note the tension that exists between anti-scald measures and the Anti-Legionella requirements of L8 to heat the storage above 60°C for one hour each day and to distribute hot water at least at 55°C and to deliver water at a least 50°C after 2 minutes.