SOLAR HOT WATER SYSTEMS

SOLAR HOT WATER SYSTEMS

Factors that will help determine what solar hot water system is best for your home.

Have you been asking yourself if you should install a solar water heater in your home and wondering what system was the best? There are several factors that must be considered before installing a solar hot water system. A professional plumber will help recommend the right system for your home.

The solar hot water system they recommend will be based on:

  • The number of people that live in your home
  • How much water your household uses
  • The time of day the water is used
  • The quality of the water
  • The roof’s pitch
  • The climate

It is important that you understand how a solar hot water system operates.

The plumber will need to know and the needs for your household. If the tank is too small then you may run out of hot water. If the tank is too large you may waste energy storing the extra hot water,

The average person in Australia uses around 80 litres per day. The appliances you have in the home will also affect your water usage.

Factors that affect your consumption include:

  • Spa baths
  • How long you are in the shower
  • The climate of the area where you live

This is a guide the Apricus solar hot water system sizes are as following:

  • 1-2 bedrooms, 22 evacuated collectors and a 250L tank
  • 3-4 Bedrooms, 30 evacuated collectors, 315L tank
  • More than 4 bedrooms, 44 evacuated collectors, 400L tank

What exactly is a solar hot water system?

  • A solar hot water system uses solar collectors mounted on the roof of the home to collect energy from the sun and use it to heat up water.

    There are different options that include:

    • Flat plate panels or evacuated tubs
    • Different boosting options
    • Natural has or LPG
    • Electric
    • Configurations of the system

    A complete kit usually includes the following:

    • Solar collector
    • Storage heater for hot water
    • Controller
    • The pump station
    • Backup energy source

Types of Solar Collectors

The solar collector takes heat from the sun and uses it to heat up the water.

There are two main collectors:

.1 Evacuated Tubes

  • They are more modern and use the latest technology
  • They are glass tubes that have an inner heat pipe that are surrounded by a vacuum
  • They have a round surface and they are able to collect more energy
  • They are good for cooler climates since less heat will be lost
  • Efficient heat transfer
  • Very durable, cheap to replace
  • Works well with overcasts skies
  • Can be put on a smaller section of the roof

These tubes are high performance and easily transfer heat from the sun into hot water. They can be used in many different climates

.2 Flat Plates

This collector uses copper pipes that go through a glass covered collector that is connected to the water storage tank and the roof. The sun will heat up the copper pipes and the water will turn hot in the storage tank.

  • Efficient when perpendicular to the sun
  • If they are not protected frost in colder climates can lead to loss of heat
  • If the plates become damaged they are expensive to replace
  • They work best when they are facing north on the roof

Which solar collector is best?

When a person is looking for a higher performance or they live in a climate that gets cold the evacuated tubes are the best for their home. They offer several advantages that the flat plate collectors do not.

Evacuated tubes are the most efficient type for collecting energy from the sun. They are durable and if there is an accident they are less expensive to replace.

How to identify the most practical setup for a solar hot water system

VIDEO TRANSCRIPTION

In this video, you’ll learn how to identify the most practical setup for a solar hot water system based on the needs of the climate, building and the householders.

In passive systems- also known as thermosiphon systems- the tank sits above the collectors. Cold water sinks into the collectors whilst warmer water rises unassisted from the collectors into the tank. The tank might sit on the roof with the collector, a close coupled system or within the roof cavity above the collector.

A gravity feed system. With these systems, the roof support structures must be strong enough to handle weight of up to 800 kilograms.

Active systems use a small pump to move water between the collectors and the tank. The location of the tank can be within the roof or on the ground.

Each type of system has advantages. A passive system is space-saving and is easy to maintain with no moving parts. An active system is unobtrusive, lightweight, can use an existing tank and the tank can be located closer to where hot water is used reducing heating loss in pipes. But the pump uses some energy.

There are two collector types to choose from; flat plate and evacuated tubes. Evacuated tubes have the advantage of receiving perpendicular radiation for a greater part of the day.

This, combined with their vacuum insulation, means good winter performance. Flat plate collectors, particularly if purchased as part of a close coupled system, can be more affordable than evacuated tube collectors. However, the prices of evacuated tubes has fallen in recent years. Collectors should ideally face true north in a shade-free position.

Facing the collectors 45 degrees from the north will result in only minor reductions in performance. The ideal inclination is the angle of latitude +5-10 degrees. Sydney’s latitude is 33.5 degrees. So an ideal angle of inclination would be around 40. However, +/- 15 degrees would still provide adequate performance.

If your collectors face true east or west, the lower the angle of inclination the better. However, to allow thermosiphon flow, you must always keep the angle above 10 degrees. For the correct sizing of your collectors and tank, consult manufacturer’s guidelines to see what is best for the climate and household.

In places with minor frost, evacuated tubes may offer in-built protection. In climates with regular frosts, indirect or closed-loop systems are the most popular and reliable form of frost protection. Instead water an antifreeze fluid is heated in the collectors. The antifreeze passes heat onto the water via a heat exchanger.

The antifreeze does not come into contact with the household water supply. Other frost protection methods are available such as frost protection valves, temperature programmable pumps and drain back systems.

In an Australian summer, water and collectors can easily approach boiling point. This can cause excessive pressure buildup and can damage the lining of vitreous enamel tanks. The Australian standard states that solar hot water systems must provide over temperature protection without draining water.

So, a temperature pressure relieve valve is not enough. The most common way to prevent overheating in the tank is by automatically stopping the circulation between collector and tank when the tank water gets too hot.

This can be done using a solar control valve or a temperature-controlled pump. See the fact sheet on the trade secrets website for more information about how to control for frost and overheating.

The solar hot water system will require boosting at some times of the year. Electric boosters use a lot of power, so make sure the booster is controlled by a manual in-house switch. This switch should include a light to indicate when on.

Boosters which have no in-house switch or are permanently on are wasteful as they often heat water to 60 degrees, water which would otherwise be heated by the sun. When advising the householder on their energy tariffs options, explain the pros and cons of each option.

A regular tariff allows boosting at any time but it won’t lead to a reduction in their bills if their previous system was electric off-peak. Off-peak will be cheaper but may not fit the hot water usage patterns of all households. If available, extended off-peak or off-peak II is often a good compromise.

Natural gas boosters have the advantage of lower emissions and running costs compared to electric boosters. And also, on subject to time of use restrictions. Install a timer on gas storage boosters to ensure the gas does not heat water which would otherwise be heated by the sun.

So, select the system for the climate and use appropriate temperature controls. Locate the collector and tank to maximize performance. Install a manual boost switch and connect to a tariff which minimize emissions and costs.

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