Achieving greater energy efficiency with thermal solar



Our country’s climate is blessed to have some of the best sunlight in the world. With the current energy situation and the ever-increasing electricity costs, we are forced to evaluate our energy consumption and implement more efficient and cost-effective solutions.

Nicole Viljoen

There are two common ways to collect energy from the sun. One is through a thermal solar collector, to gather the sun’s heat and the other is a photovoltaic (PV) solar system, which converts the sun’s energy into electricity. In the case of solar thermal, the conversion efficiency is much higher than PV. Another advantage is that solar thermal panels only cost a small fraction of what PV panels cost per square meter. On the other hand, PV is more expensive and less efficient but the electricity generated from PV can be used for more than just heating up water.

Into detail

A thermal solar system can provide approximately 60% of the energy required each year for heating domestic hot water (DHW). The key element of a thermal system is the solar thermal collector, which absorbs solar radiation from the sunlight. The purpose of the collector is to efficiently convert the sunlight into heat. The heat is transmitted to a fluid, which transports the heat to the heat exchanger via pumps with minimum heat loss. The exchanger transfers the heat into the geyser. The distance between the collector and the geyser should be as short as possible to minimise heat loss.

There are two main types of solar thermal collectors available. The first, an evacuated-tube collector is made of parallel glass tubes. Each tube contains two glass tubes, between the two glass tubes there is a vacuum which allows small heat loss. The absorber is included in a tube. The second type is the flat-plate collector which comprises an insulated box with a glass or plastic cover on the top and a solar absorber located at the bottom. In comparison, evacuated-tube collectors are more expensive than flat-plate collectors. However, they can achieve higher efficiencies.

Achieving optimum heat yield

The integration of solar thermal systems requires precisely matched individual components to achieve optimum heat yield and to keep costs under control. This must be supported by the right system engineering. Solar water heating systems almost always require a backup system for cloudy days and times of increased demand and therefore most solar water heaters require a well-insulated storage tank or DHW cylinder. Dual mode DHW cylinders work to heat the DHW with separate indirect coils that are connected directly to the solar thermal system. DHW is also heated by a boiler via an indirect coil arranged in the upper section of the cylinder.

The demand for hot water varies considerably from household to household. The number of occupants has to be taken into account, as well as their bathing and showering habits. For example, if three members of a family set off for work and school at the same time, lots of hot water needs to be continuously available for the shower in a short space of time. Those who prefer a bath will also want to have enough hot water to fill the tub. The DHW cylinder should also be able to provide sufficient water if hot water is drawn from more than one outlet at the same time, in apartment blocks for example.

Vitocell DHW cylinders fulfil these requirements in every respect and can also meet every aspiration where equipment levels are concerned. In all instances, the installation of a solar thermal system is recommended to save energy and heat the water without cost.

Thermal range

Energas offers Viessmann’s Solar Thermal range. Installers and end-users are urged to recognise the role of hot water storage in optimising environmentally-friendly installations. Viessmann has introduced two new floor-standing Vitocell 300-V DHW cylinders, with capacities of 160 and 200 l, and are twice as energy efficient in terms of standby losses as the industry norm.

Both new versions of the Vitocell 300-V replace the previous A rated models, and both are suitable for domestic installations with boiler outputs up to 80 kW. Higher DHW demands can be accommodated by combining several Vitocell 300-V cylinders into cylinder banks with common headers.

The 300-V’s exceptional heat retention is made possible by using a highly-effective vacuum panel insulation as well as the very efficient Polyurethane hard foam. Heat losses are merely 0,7 kWh per 24 hours for the 160-litre model and 0,75 kWh per 24 hours for the 200-litre model.

The new 300-V combines unmatched energy efficiency with high performance. The indirect heating coil is larger than in most common cylinders and drawn all the way down to the cylinder floor to heat the entire water content. Heat-up time from 10 to 60 degrees is just 20 minutes for the 160-litre cylinder and 24 minutes for the 200-litre cylinder.

The low pressure-drop of the heating coil, at only 15 millibars, is approximately 35% lower than a typical competitor cylinder. This negates the requirement for oversizing the circulating pump; specifying a smaller pump will save electricity. Maximum hot water flow rates are 24 and 34 l per minute respectively.

The 300-V’s insulation package can be removed for easy handling. Transportation and installation are also made easy by the 300-V’s low weight and compact dimensions. Both 300-Vs are 581 mm long and 605 mm wide, with the smaller-capacity model measuring 1189 mm in height and the larger-capacity model 1409 mm.

Regardless of the size of your home, how many people live there and how much hot water they use, our Vitocell range will have the right cylinder for your DHW heating system.

Send your comments to energize@ee.co.za

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Source: EE plublishers

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