Tapping the green potential of hot water

June 2010 - With the increasing emphasis on environmental performance, the search for the most efficient and effective water-heating solution for multi-dwelling buildings becomes more critical. Stiebel Eltron Australia’s sales director, DARREN FLETCHER, discusses the best options in terms of efficiency, installation, running costs, and environmental performance.

Multi-dwelling apartment buildings present a number of options for delivering hot water services. The two main alternatives are centralised boilers, used to service the whole building, and individual stand-alone instantaneous water heaters installed in each apartment.
With increasing pressure for new buildings to achieve green targets, property developers face the mounting challenge of evaluating which of these options is most suitable. Measures such as ‘efficiency’, ‘cost’ and ‘environmental performance’ are commonly used interchangeably without a full comprehension of their implications. If an informed choice is to be made, it is important to understand what these terms mean and how they interrelate.
In Australia, centralised hot water services for apartment buildings tend to be gas-fired, while stand-alone instantaneous hot water units can be either gas-fired or electrically operated. Gas-fired hot water systems – whether centralised or stand-alone instantaneous – have burner heating efficiencies of 80 to 85 percent. Electric instantaneous hot water systems, by comparison, have a heating efficiency of 99.5 percent.
Clearly, in terms of heating efficiency, electrical systems win hands down. However, there are other factors that contribute to the overall system efficiency and environmental performance: system architecture, installation quality, and ‘cleanness’ of energy source. Operating costs are also a powerful decider in system selection.
It is necessary to weigh up all these factors in order to determine the best option from both environmental and cost perspectives. As will be seen, given the global and national push towards renewable electricity sources, electrical water heaters present a particularly compelling solution for the future.

CENTRALISED SUPPLY
Centralised gas-fired hot water heating systems are generally assumed to have the lowest carbon footprint of the three systems available, but this is not necessarily the case. Since they operate continuously, regardless of demand, centralised gas-fired systems tend to be inherently inefficient in their design and can be costly to operate. Typically, a centralised hot water plant comprises a ring-main that extends throughout the building, with individual feeds radiating to each individual apartment (see Figure 1). With this type of system, heat is lost from the storage tank and from the long pipe-runs making up the ring-main and the apartment feeds.

One notable feature of the reticulation architecture of these centralised systems is that the 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.
Centralised gas-fired systems also often present a more expensive initial cost for the 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 SAVINGS
By comparison, stand-alone instantaneous systems offer many advantages. 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. Furthermore, with 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 at the outlet.

Instantaneous hot water units also benefit from lower installation costs when compared to centralised systems, as the requirement for large items of plant and reticulation infrastructures is eliminated (see Figure 2). With fewer components, instantaneous systems often prove more reliable than more complicated centralised systems. They also minimise the impact to residents in the event of equipment malfunction. As a worst-case scenario, a breakdown in an instantaneous water heater may leave a single apartment without hot water. A system malfunction for a centralised hot water system, by contrast, has the potential to cause the loss of hot water for an entire building.

These stand-alone instantaneous hot water units are generally owned as part of the apartment, and, as such, the residents only pay for their own water use and servicing. Conversely, centralised hot water systems are usually owned by the building’s body corporate, with maintenance and operation costs often averaged out and passed on to the building occupants through the body corporate fees. This can lead to low-consumption water users effectively subsidising the high-consumption users within a building, unless hot water meters are installed to aid accurate billing for hot water use by each apartment. Even with the aid of meters, the end users still end up paying for the inefficiencies of the hot water system, as these are incorporated into the cost of the hot water used.
The choice between gas-fired or electrically operated instantaneous water heaters has subtly different implications. While the service and infrastructure requirements of instantaneous gas-fired hot water heaters are greatly simplified compared with centralised gas-fired systems, the units still require annual servicing, adding to the maintenance costs. Likewise, while instantaneous gas water heaters bypass the need for a reticulation system, individual gas feed pipes – complete with meters – are required for each apartment and significantly increase installation costs.
For the apartment itself, instantaneous gas-fired water heaters typically need to be located externally for safety reasons and for flue requirements. This works well where apartments have balconies, but for buildings without a suitable accessible and usable external area, this option may not prove viable. Given the requirements for external placement, the water heaters will not necessarily be able to be installed adjacent to the bathroom or kitchens where the hot water is needed, leading to water wastage through longer pipe-runs.

THE ELECTRIC EDGE
Three-phase instantaneous electric hot water heaters, on the other hand, require a simpler infrastructure that allows greater flexibility – and arguably lower life-cycle costs. These units tend to be smaller than their gas-fired counterparts, and benefit from greater heater efficiency. Moreover, without the requirements for gas feeds or flues, these units can be positioned exactly where they are needed in an apartment. This enables pipe-runs from the heater unit to the application to be minimised, and in some instances virtually eliminated.

Instantaneous electric hot water heaters achieve the lowest levels of water wastage of any hot water system available, partly through their capacity to reduce delivery pipe lengths, and partly through the ability to heat water more quickly than competing systems. A study conducted by Carbonetix Climate Change Solutions has shown that a typical apartment, fed from a centralised gas-fired system, wastes 7000 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 just 1600 litres.
Of course, the performance and convenience of instantaneous electric hot water systems need to be weighed against the running costs and environmental performance that these systems offer. The study by Carbonetix indicated that for a typical 25-apartment building in Victoria a centralised gas-fired hot water system delivers 14 percent less greenhouse gas emissions than instantaneous hot water systems for typical usage in this state. However, if hot water usage is kept to an achievable 29 litres per day per person, electric hot water heaters become the greener choice.
The Carbonetix study purposefully targets Victoria, given its reputation as the worst producer of greenhouse gases per kilowatt hour in Australia – a direct consequence of using lignite (brown coal) to fuel the state’s electricity-generating power stations. For states using anthracite (black coal) as the fuel of choice for electricity generation, greenhouse gas emissions immediately drop by around 25 percent, thereby ensuring electrically heated hot water systems will outperform centralised gas-fired plants, regardless of the hot water usage figures.
Given that electricity generation in Victoria has historically had a poor environmental performance record, there is considerable potential for improvement. Renewable sources of electricity generation are expanding every year, and it is expected that legislation will help persuade electricity providers to continue seeking ways to increase the sustainable proportion of the energy they supply. Over time, with a greater proportion of electricity being sourced from renewable sources, the overall carbon impact of electricity generation has the potential to fall. Gas-fired appliances, by contrast, offer much less scope for further reducing 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 blocks. Here, developers have the opportunity to minimise equipment and installation costs, while delivering efficient, reliable and environmentally responsible hot water for building residents long into the future.

Darren Fletcher is Stiebel Eltron Australia’s sales director.
The Stiebel Eltron group is a global designer and manufacturer of innovative water heating, ventilation, air-conditioning and refrigeration systems technology, headquartered in Holzminden, Germany. Its broad spectrum of solutions includes instantaneous electric water heaters, heat pumps, space heaters and water filtration systems.
The Australian division of Stiebel Eltron is headquartered in Melbourne, supported by a network of offices in Sydney, Brisbane and Adelaide, along with distributors in Perth, Hobart and Auckland, NZ. All offices are equipped with comprehensive sales, service and technical support teams.
Stiebel Eltron Australia’s core product focus is on instantaneous electric water heaters, point-of-use hot water and filtration systems, and heat pumps for commercial and residential sectors.

More information
Stiebel Eltron Australia www.stiebel.com.au