This Article was originally published in the April-May 2024 Issue of  NZ Plumber Magazine:

https://issuu.com/nzplumber/docs/nz_plumber_apr-may24_lr_singles

The insulation of the hot water distribution pipework and hot water recirculation ring mains is an extremely important component of a hot water system install and corresponding pipework, as hydraulic consultant Jordan Ross explains here.

AUTHOR: JORDAN ROSS, ENDEAVOUR CONSULTING

The hot water cylinder (HWC) outlet pipe is potentially the point of the hot water system’s greatest heat loss, as this pipe will contain the hottest water from the cylinder. Generally, the outlet is on top of the cylinder, though this is not always the case. NZBC G12/AS1 requires one metre of copper pipework between the cylinder outlet and the tempering valves. This requirement, along with the first pipe drop of 250mm creates a heat trap.

How do I meet Building Code requirements when the HWC set ups vary?

NZS 4305:1996 Energy efficiency – Domestic type hot water systems requires that hot water distribution pipes must be thermally insulated between the storage water heater and one or more of the following:

• For horizontal pipe, to not less than 2m

• To the end of the first continuous 2m of horizontal pipe, if the pipe has not followed a downward direction

• To the first pipe drop of at least 250mm, ie, heat trap. The insulation shall extend at least 150mm past the top of the heat trap.

  What does all this mean? If no heat trap is provided: for horizontal pipework, insulation is provided to not less than 2m, and to the end of the first continuous 2m of horizontal pipe if the pipe has not followed a downward direction.

  My preferred option is the heat trap with insulation as I think it presents a tidier install, ease of maintenance, and prevents excessive heat losses.

What about hot water flow and return pipework on a recirculation ring main? '

The hot water flow and return pipework also needs to be insulated to meet the requirements of NZS 4305.

With a hot water recirculation ring main, the hot water flow and return pipework will recirculate through the system, keeping the water hot and reducing the dead leg lengths of the hot water pipework to the fixture to ensure they are compliant with NZS 4305 and remain less than 2 litres.

Hot water flow and return pipework is more expensive to run than a conventional hot water system with dead leg pipework to the fixture. Some of the reasons for choosing a hot water recirculation ring main system might be:

• The remote location of the hot water plant to the fixture locations to keep the pipework dead leg lengths short and compliant

• Client expectations for hot water wait times to the fixture

• Building use and space allocation for hot water plant within the building footprint—for example, a hotel.

What do heat losses within a recirculation ring main cost me?

The heat losses within the ring main can be calculated using the manufacturer’s tech data for the insulation, which will give the heat lost per metre to the corresponding pipe size and operating temperature. So, the cost of the ring main relative to the heat lost per year can be calculated by multiplying the total kilowatts lost by the cost of power.

There are some things that can be done to limit this cost:

• Increase the thickness of the insulation to reduce the heat lost per metre (this should be weighed up with the increase in capital cost)

• Put a time clock on the recirculation pump so it reduces the run time in a 24-hour- period to the times that hot water is going to be used.

Why are good installation techniques important for hot water pipework insulation?

It’s important to reduce the heat losses throughout the system, not only from a cost perspective but also so the return temperature is not such that the hot water plant is having to work too hard to maintain excessive losses from the heat lost within the recirculation ring main.

The biggest potential heat loss comes from poor installation practices. The most common areas to look out for are:

• Bracketing: There are a couple of ways to tackle this. The best is to use a supporting block between the clip and the pipe. This is generally a proprietary item, and the insulation can butt up against the block and be wet sealed with glue. The second way is to have an oversized secondary layer of insulation around the clip, and the insulation on the pipe to prevent the heat escaping. I have often seen it done poorly, where the clip is taped to make it appear that the insulation carries through the clip consistently. This will lead to excessive heat loss.

• Valving: Due to valving being an irregular shape to the pipe, the insulation may need to be made up of different cut pieces, and tube sizes cut specifically for the sized valve with adhesive applied to ensure the pipework and the valve are completely enveloped by the insulation.

• Bends and tees: Installing insulation around bends and tees takes experience. The manufacturer gives good direction on the proper angle cuts required to make up segmented bends, tee pieces or oversized bends, tees and reducers.

• Knives: A sharp knife must always be used and kept at a low angle when slitting the tube.

• Glue: It’s poor practice to rely on tape rather than glue. A thin layer of adhesive should be applied to the two cut edges using a short bristle brush along the entire tube length and allowed to touch dry.