Hot water energy saving - non-electrical devices and methods

See here for electrical devices and methods.

Here is a small amount of information about the gains you can achieve and a few links to get you started in this area. Energy gains can be made in electric, gas and solar systems.

Hot water cylinders

Hot water cylinder manufacturers and many energy efficiency advice websites will tell you "newer" hot water cylinders will not benefit from additional insulation like a cylinder insulation wrap. This often repeated general advice is frequently incorrect. In reality it depends where the cylinder is installed and the quality of insulation present in the cylinder.
  • If your cylinder is in an uninsulated or inadequately insulated area like an underfloor area, basement, or attic - during cold periods you will see massive gains from using a cylinder wrap.
  • If your cylinder faces at least one external wall - you are likely to see worthwhile gains from wrapping your cylinder - especially if the external wall is not well insulated to begin with.
After insulating the cylinder you may wish to increase the efficiency of the enclosure cupboard if the enclosure is used for drying damp items (see below). Insulating the cylinder and pipes leading from it will not necessarily make the cylinder enclosure (hot water cupboard) ineffective for drying purposes.

Some cylinders are specifically designed for external or very cold area installation and will have much more effective insulation properties.

Hot water pipes

The easiest pipe insulation to fit is a soft-polyurethane tube material which fits over the existing pipe. This material usually comes in short lengths and can be cut to size. This material has a self adhesive tape seam running down the length of the soft tube and provides an excellent heat retaining seal. Pipe insulation without this self sealing seam must be cut down its length before fitting to an existing pipe. If the seam is not sealed after installation then some insulation value may be lost.

Cylinder header pipes

Many cylinders use a header pipe system leading to the roof to regulate pressure in the cylinder. If the header pipe is uninsulated then the water in this pipe will cool. Allowing this water to cool creates several energy loss conditions. This cold water is released back into the system when a tap is turned on. For this reason insulation of the entire length of the header pipe is worthwhile. To a lesser extent the cooling water column in the header will act as a heat loss conductor for water remaining in the cylinder. 

Header system tech details: The header system provides simple and low maintenance pressure regulation. The length of the header pipe effectively regulates the pressure of the water remaining in the cylinder. The header pipe usually follows a straight line vertically to the roof. About 10kpa pressure per meter of header pipe is generated in the cylinder. An intake valve (looks like a flying saucer) is used to regulate the maximum pressure entering the cylinder from the cold water system. In fault situations where the intake valve fails or becomes partially blocked by debris excess pressure will exist in the system. In this fault situation - which can be severe or minor - excess pressure (hot water) will be released from the top of the header pipe. This is a common cause of high energy use in hot water systems and can be easily fixed by cleaning or replacing the intake valve. This is a job for a plumber. Other systems use a pressure relief valve (may also look like a flying saucer) with a drain instead of a header pipe. The NZ G12 building standard [September 2010] (figure 5 onwards) has details of possible hot water system configurations.

Hot water outlet pipe insulation

Insulation of hot water pipes will cause the water in the pipes to remain warm (and even hot) for a very long time. This leads to very significant gains. Significant energy can be lost through cooling between the cylinder and an outlet/tap. This is especially true when hot water pipes pass through uninsulated underfloor areas and basements. If water is warmer when it reaches the outlet then less hot water will be needed to achieve higher temperatures in applications where hot and cold water are mixed. This includes: showers, kitchen sinks, etc.

Most people like to wash their hands in warm or hot water. This is especially true in cold weather. Most users will wait for water flowing from the tap to become warm before beginning to wash. The same is true when using a shower. For this reason insulation of hot water pipes can reduce water resource waste and billing. Users will not need to wait so long for a comfortable temperature.

Insulating the entire length of all hot water pipes is worthwhile. This is true for gas, electric, and solar systems.

Hot water cupboards used for drying and dry storage

Hot water cylinder enclosures are often used for drying damp items and used for dry storage. Many enclosures used for this purpose are not optimised for this purpose at all. Optimisation of enclosure drying properties can be important after fitting cylinder wrap insulation and pipe insulation within the enclosure.

Retaining more heat in the enclosure will increase drying efficiency. A reflective barrier (thin insulated foil) takes up very little space and will be very effective in retaining heat in the enclosure. The reflective barrier can also be fitted over the inside of the enclosure door. Even simple methods to fix the foil in place like drawing pins or push pins can be very effective.

Installing wooden shelves/racks above the cylinder can make drying more effective. Shelves & racks made from finished softwood (like pine) will slowly absorb and dissipate moisture - this will increase drying efficiency.

Insulation of the cylinder and pipes within the enclosure will not prevent heat from the cylinder and pipes reaching the enclosure but it will slow down the rate of transfer. Retaining heat in the drying enclosure becomes more important.

Hot water energy recovery

Energy leaving the house system after being used in hot water for a shower, sink or dishwasher is usually lost. This heat energy can be recovered and regained without using the water itself.

Hot water energy recovery devices work by transferring the heat energy from outgoing hot water into the incoming cold water entering the hot water heating system. Water entering the heating system is now warmer to begin with and therefore less energy is required to heat this incoming water to the required temperature before using it.

Many systems are available in New Zealand. Two for example:

Spirex Energy Drain

Different sizes available. Supports horizontal or vertical mounting. Easily added to existing systems. 

Available from Vaportec Systems  - follow the link for performance and energy recovery statistics.

GFX Gray Water Heat Recovery System

Different sizes available. Efficiency increases as size goes up.

Available from Quadrix Energyfollow the link for pdf's on performance and energy recovery stats.

Hot water energy conservation

In an efficient system - reducing the total volume of hot water used will reduce the energy cost required to heat it. A good quality low flow or adjustable flow shower head will maintain shower quality and enjoyment while reducing total heat energy used. Users often remain in showers longer during cold weather and use more hot water energy to attain warmth. Products like Shower Dome retain heat within the shower enclosure allowing users to attain warmth faster with much less energy input.

Standards compliance

Aspects of hot water systems in NZ must comply with standards set by the department of building and housing.

The standards [September 2010] state: "The delivered hot water temperature at any sanitary fixture used for personal hygiene shall not exceed: (a) 45°C for early childhood centres, schools, old people’s homes, institutions for people with psychiatric or physical disabilities, hospitals, and (b) 55°C for all other buildings" and "[...] the storage water heater control thermostat shall be set at a temperature of not less than 60°C to prevent the growth of Legionella bacteria".

Effectively this means a tempering valve (mixes hot and cold water) is required to ensure the (minimum) 60°C storage temperature is always a maximum of 55°C (or 45°C) when it arrives at the tap. The standards indicate it is acceptable to supply higher temperatures to kitchen appliances and laundry appliances.

[Note: This section requires editing to indicate these standards must be applied when installing new showers / faucets / bathrooms, but might not need to be applied when modifying the hot water system. Checking with Dept..]   

Technical information and research

The BRANZ Household Energy End-Use Project (final report) is a great source of technical information and up to date research on energy use in domestic hot water systems in New Zealand.   


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