Stiebel Eltron

Environmental performance, efficiency, installation quality and running costs are key factors in selection of the most efficient and effective water-heating solution for multi-dwelling residential buildings. In addition, consumption and wastage of water-a finite natural resource-must also be part of the equation for determining the most suitable option.

Energy efficiency and sustainability are becoming increasingly important to all parts of society-from the largest businesses to the private home. Increasing regulation and end-user demand is for activities to have minimal impact on the natural environment. The cost of energy is a significant domestic outgoing and a simple and direct way an individual can lessen their impact is to reduce the resources consumed in their daily life; in particular water wastage in hot water systems.

In Australia, centralised hot water services for apartment buildings tend to be gas-fired, while stand-alone instantaneous units heat water either gas-fired or electrically. In terms of heating efficiency, electric instantaneous hot water systems are a better option because they have a heating efficiency of 99.5 per cent when compared with gas-fired hot water systems that have burner heating efficiencies of 80 to 85 per cent.

Electrical systems have the advantage in terms of heating efficiency, but there are other factors that contribute to the overall system efficiency and environmental performance: system architecture, installation quality, ‘cleanness' of energy source. Operating costs must also be considered in system selection. While most environmental impact studies focus solely on energy usage, water wastage becomes an important factor to be considered given the fact that most parts of Australia regularly face water restrictions.

According to Darren Fletcher, Sales Director at Stiebel Eltron, there are several aspects to the cost of producing hot water. "While fossil fuels are consumed to generate electricity or burned directly to heat water for domestic use, the greater cost is the use and wastage of water in the systems."

Architects and builders face mounting pressure to make the buildings they erect as ‘green' as practical and meet the challenge of evaluating which hot water system is the most suitable. The alternatives are centralised boilers-servicing the whole building-and individual instantaneous water heaters installed in each apartment. Multi-dwelling residential developments provide an ideal setting in which to demonstrate the water saving and other benefits of instantaneous hot water systems.

According to Dr Richard Evans, President of the Australian chapter of the International Association of Hydrogeologists, one third of Australia's water supply is from ground sources. "There is no doubt that water is a finite resource. Ground water levels have been over-developed in certain regions, where utilisation has exceeded the recharge rate. We need to be encouraging water efficiency at all levels: in agriculture, business and at home."

To simplify the infrastructure requirements of an apartment block it can sometimes be better to select electric appliances to remove the need for gas feeds to each apartment. An instantaneous electric hot-water solution can be positioned exactly where it is needed without the restrictions associated with gas feeds, flues or venting.

"Apartment buildings generally allow a choice of instantaneous electric, instantaneous gas, or centralised gas water heating systems," Fletcher said. "The instantaneous electric option has the least infrastructure requirements, and therefore represents the most cost-efficient choice for installation."

Centralised supply
Centralised gas-fired hot water heating systems are generally assumed to have the lowest carbon footprint of the three systems available, but by having to operate continuously-regardless of demand-centralised gas-fired systems can be inefficient in their design and costly to operate. Typically, a centralised hot water plant comprises a ring-main that extends throughout the building, with individual feeds to each apartment. With this type of system, heat is lost from the storage tank and from the long pipe-runs.

Water in each of the apartment feeds is often significantly colder than the water circulating in the ring-main. This necessitates draining the cooler water from the feed-often referred to as ‘dead-legs'-every time hot water is wanted, resulting in significant water wastage. While most environmental impact studies focus solely on energy usage, water wastage becomes an important factor to be considered given the water restrictions in force in many Australian states.

Such systems also often present a more expensive initial cost for a property developer, given the requirements for a dedicated plant room, large commercial gas boilers, hot water storage tanks, circulating pumps, and the reticulation pipework. Moreover, these systems are often associated with higher maintenance costs.

Instantaneous electric advantage
Many advantages are available through choosing stand-alone instantaneous systems. As water is only heated at the time of use, energy is not wasted in maintaining a stored volume of hot water, and operating costs are reduced. With the heating units located closer to the point-of-use, pipe-runs are shorter and less water is wasted by the user while waiting for sufficiently hot water to arrive to the outlet. Studies have shown that a typical apartment, fed from a centralised gas-fired system, wastes 7,000 litres of water over the course of a year, simply through waiting for hot water to arrive at the tap. An instantaneous electric water heater system can reduce this down to less than 1,600 litres.

Renewable sources of electricity generation are expanding every year, and proposed legislation will encourage increasing the sustainable proportion of the energy power companies supply to consumers. Over time, with a greater proportion of electricity being produced from renewable sources, the overall carbon impact of electricity generation has the potential to fall. In contrast, gas-fired appliances offer much less scope for reduction of greenhouse gas emissions into the future.

Property developers need to weigh up the cost effectiveness and the environmental performance of the various water heater technologies to determine the most appropriate hot water service option for new multi-dwelling residential blocks. Here, developers have the opportunity to minimise equipment and installation costs, while delivering efficient, reliable, water saving, and environmentally responsible hot water for building residents long into the future.

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Instantaneous hot water units benefit from lower installation costs than centralised systems, due to the ability to minimise requirements for large items of plant and reticulation infrastructures.