In Hot Water

In Hot Water
August 21, 2013

Water heating typically makes up around a third of a typical Kiwi households energy bill and with the cost of energy continuing to rise, the choice of water heater is now more important than ever.

Whether you are building, renovating or simply improving your home, it is worth doing your research and looking into the type of hot water system that best suits you and your family’s needs.

But before we start talking to you about which heater is the best or most efficient, it’s important to remember that small lifestyle changes can go a huge way towards reducing your energy bills without having to make any big purchases, take a few of the following tips for example:

  • Have your hot and cold taps separate (ideally so that the run to central spout). With a combined mixer, most people leave the tap in the middle out of convenience so it always draws hot water when you turn it on.
  • Only use cold water for rinsing your dishes or washing your hands. Better yet, try to only wash clothes in cold water if you can help it
  • Turn off the water heater when you go on holiday.
  • Have showers instead of baths and keep your showers relatively short (showering generally uses about half the water that running bath will use)
  • Choose water-efficient household appliances; look at a products WELS water rating, the higher the number of stars it has, the cheaper to run and more efficient it’ll be
  • Look at installing flow-restricting showerheads or tapware
  • Fix any dripping tapware (one dripping tap can waste almost 5500litres of water a year!)
  • If building or renovating, consider installing a thermally efficient (and environmentally friendly) pipe such as ‘aquatherm green pipe’, or by wrapping your pipes in insulation (called ‘lagging’ in plumbing terms).
  • Again, if you’re building, try and group all of your hot water using areas together, to reduce the heat loss as hot water flows through your plumbing.

What type of water heater is best for me?

To make significant efficiency gains over and above traditional water heating systems, the two commonly available technologies are boosted solar and heat pump water heaters. This month we’re going to take a look at few different types of hot water heating systems. It seems like every man and his dog has heard about the positives of installing a solar water heating system; that a solar heating system will save you money or that a solar water heating system is better for the environment. So let’s start by having a look at what a solar water heating system actually is.

Solar water heating

A solar hot water system absorbs the energy from the sun in collector panels located on the roof of your home, and transfers that energy to the water stored in your hot water cylinder. When there is not sufficient energy from the sun to heat the water in the cylinder a booster system (either electric, gas or wetback) is used to heat the water to the required temperature. The core of a solar water heater is a solar collector and a storage tank. A solar collector is basically a glazed, insulated box with a dark-coloured interior and, usually, a bunch of tubes or passageways for water flow. (Glazing is a coat of material, typically glass, which aids in heat retention.) The solar collector turns the sun’s radiation into heat. A storage tank is exactly what it sounds like. It holds the water.

That’s the basic setup, and some systems aren’t much more complicated than that. There are many distinctions among solar water heaters; flat panel or evacuated tube, split system or tank on roof, direct or indirect, passive or active? All of these options have benefits for particular solar applications but the number one factor to ensure efficiency is the installation. The roof should face north and remain unshaded throughout the day and if it is not at the correct pitch, a stand will be required.

An active heater uses electrical pumps and controls to move water around the system. A passive heater uses nothing but forces of nature. Passive is the simpler of the two.

There are two primary types of passive systems:

  • Batch: This is as uncomplicated as a water heater gets. It’s just one or more water tanks inside a solar collector (no tubes in this one). The water warms up right inside the tank, and either gravity or natural convection (the tendency of hot water to rise) moves water from the tank to a home’s pipes.
  • Thermosiphon: The water tank is separate from the solar collector. Cold water moves through the tubes of a solar collector, and natural convection pumps the resulting hot water into a storage tank. From the storage tank, the water travels into the home’s water pipes.

Active systems typically fall into one of three categories:

  • Direct: Water moves through the solar collectors and into a storage tank with the help of electrical pumps and controls.
  • Indirect: Instead of heating water, the solar collectors heat a “heat transfer” fluid, such as antifreeze. The antifreeze then flows into the sealed piping of a heat exchanger, where it is surrounded by water. The water picks up the heat from the antifreeze (but never mixes with it), and is then pumped into a storage tank.
  • Drainback: A drainback system is like the indirect system except that it uses distilled water as the heat-transfer liquid, and it has a separate “drainback” tank for the distilled water. Pumping all of the heat-transfer liquid out of the system and into an interior tank makes it ideal for colder climates, since the liquid isn’t exposed to extremely cold weather.

The benefits of solar water heating:

  • Hot water throughout the year: the system works all year round, though you’ll need to add. an electric, gas or other booster connected to your solar water heater for when the sun can’t heat enough water to meet your needs
  • Cut your bills: sunlight is free, so once you’ve paid for the initial installation your hot water costs will be reduced.
  • Cut your carbon footprint: solar hot water is a green, renewable heating system and can reduce your carbon dioxide emissions.

Specifying the right products for your household’s requirements in the right combination is the key to ensuring that you will not have to sacrifice comfort just because you have chosen the green option. Contact Rinnai, or Plumbing World for information specific to your situation.

Next up, we introduce….

Heat pump water heating (HPWH)

Heat pumps use the same technology to heat water as is used to heat rooms, they use energy from the outdoor air or ground to heat water that is then stored in insulated hot water cylinders (think of giant thermos flask). Heat pump systems only use electrical energy to ‘move’ the heat – they don’t actually ‘make’ heat. This makes heat pump systems much more efficient than traditional electric or gas water heaters.

There are two main types of HWPH:

  • all-in-one (integral) system; where the heat pump is part of the hot water cylinder, this is located outside (preferably near to the bathroom, thus reducing the piping distance between the source and destination of your hot water) and has the added bonus of freeing up your hot water cupboard.
  • split system; where the heat pump is located outside and the hot water cylinder (which can be a modern electric cylinder) is located inside the house. Split models use an outdoor heat pump unit, which looks similar to a space-heating heat pump. A small pump then circulates water between the outdoor heat-pump unit and the hot-water cylinder. There are limits on the length of the piping from the heat pump to the water cylinder, but the shorter distance the better.

There are few things you should consider when deciding on whether HWPH is right for you

  • The warmer the outside air in your region, the more efficiently your HWPH will run. They tend to work best in areas where the ambient outdoors temperature is above 7° Celsius. They do work in lower temperatures or in areas where the temperature falls below freezing, but they may require an additional electric booster or element that can increase your running costs.
  • According to Consumer NZ, a well installed HWPH can reduce your water heating bill by two thirds but they are relatively expensive to install.
  • HWPH can be very noisy, you don’t want to install the external unit outside your (or your neighbours) bedroom.

Further on down the line

The cheapest way to be more efficient is to change your habits. Wash your hands in cold rather than hot water. If you like baths, try saving them for special treats. Try to reduce the length of your showers – every extra minute of showering adds up to around an extra $80 per year in water heating.

Every little bit counts, both towards your bottom line and the planet’s.


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