‘Energy efficient’ water heating

When a building design includes a large number of individual spaces such as apartments or offices, developers are always on the lookout for ways to reduce construction costs. There will always be a project expense for supplying hot water to a large number of units, but the installation and ongoing costs can be minimised with the appropriate choice of heating system. The main options for supplying hot water to apartments in medium- or high-density developments are a centralised gas-fired water heating system or instantaneous heating systems installed at, or very near, the point of use.

In a centralised system, large boilers and storage tanks are installed along with pipework to the apartments. Where a development has several hundred apartments, centralised hot water systems require multiple boilers and all pipework must be duplicated for the hot and cold supply. Each floor also requires two sets of pressure balancing valves. The hot water pipes to each apartment are often referred to as ‘dead-legs’, meaning that the water often cools down while waiting to be drawn off.

Such systems also 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 pipe work. These systems are often associated with higher maintenance costs.

The alternative to a centralised system is ‘instantaneous’ heating at the point of use through Stiebel Eltron DEL units. In this scenario, a cold water feed is run to each apartment and a water heater installed so that the length of any ‘dead leg’ is significantly minimised.

There are many advantages in choosing stand-alone instantaneous hot water units: water is only heated at the time of use and energy is not wasted in maintaining a stored volume of hot water. 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 hot water to arrive at the outlet. If only a cold-water feed has to be provided, the commissioning engineer only needs to configure the pressure balance once on each floor using pressure valves and pumps. The cold water feed can be run to each apartment and then connected to the water heater.

Vogue South Yarra, a large mixed development of retail outlets and 498 residential apartments in a 31-storey tower in inner-Eastern Melbourne, is a landmark project for builder Hickory Group Pty Ltd. Installing Stiebel Eltron electric water heaters for all the apartments streamlined the installation of the building’s plumbing and contributed to the project being completed on time and within budget.

The project team was lead by Hickory Group Construction Manager George Abraham. “At that time, Vogue was our flagship development,” he said. “It was the largest project we had undertaken up to that time and using instantaneous hot water units made our fit-out sequence more efficient.”

According to Alistair Guss, Director of MacCormack Associates Consultants, the engineering consultants for the Vogue South Yarra project, the work was kept to schedule because the offices and apartments could be completed in stages. “During construction of the podium levels and tower, groups of apartments were completed and handed over to their owners. This allowed the plumber to work to the builder’s schedule on an apartment-by-apartment, level-by-level basis,” he said. “If we had a centralised system we would have had the equipment fully plumbed and water circulating through floors that were still in construction.”

Stiebel Eltron Sales Director Darren Fletcher agrees. “Apartment developments generally allow for a choice of instantaneous electric, instantaneous gas, or centralised gas-plant water heating systems,” he said. “The instantaneous electric option has the least infrastructure requirements and therefore represents the most cost-efficient choice for installation.”

According to Chris Barrile, the Construction Manager for Vogue’s hydraulic installation engineers, BP Plumbing, “Stiebel Eltron was more cost effective as the installation of the units was not as labour intensive. We were not required to a fit flow and return system throughout the building, just a cold water supply to each apartment.”

Water in each of the apartment feeds is often significantly colder than the water circulating in the ring-main. Depending on the length of a dead-leg, simply draining the cooler water from the feed every time hot water is wanted results in significant water wastage. While most environmental impact studies focus solely on energy usage to heat water, water wastage is an important factor to be considered given the water restrictions in force in many Australian states.

One solution for keeping water hot in a pipe is to install a ‘heat trace’ option. “A heat trace is a simple plastic-coated wire attached along the length of each dead-leg that warms the copper pipe to keep the water at a higher temperature,” BP Plumbing’s Barrile said. “However, this is a very expensive option as the power is on 24 hours per day, seven days a week.” Instantaneous water heaters eliminate the need for keeping water hot in apartment feed pipes.

Apportioning the costs of hot water in an apartment building can be inequitable. With a centralised hot water system, water is constantly circulating in the pipes throughout the building, ready to be drawn off by each apartment. According to MacCormack’s Guss, there is usually a ‘service to property charge’ that owners pay to cover the cost of reading a meter, preparing the bill, sending out the bill and collecting payment. “You pay for this whether you open a tap or not,” he added. “The final running costs of an instantaneous system are also much reduced as there is no legacy requirement for the body corporate to service and administer any centralised plant and equipment and apportion costs to each unit.”

Often, the cost of hot water is simply divided by the number of apartments. However, one apartment might use hot water for two hours but another might use 20 hours and still pay the same amount. Hickory’s Abraham stated, “Having a Stiebel Eltron unit in the apartment gives an accurate picture of consumption and you are charged for what you use, which is fair.” Such an arrangement is a true ‘user pays’ solution.

The Stiebel Eltron DEL unit.

Maintenance and repair costs are also less for instantaneous water heaters. “With a central system, we would have to go in and spend hours trying to isolate the cause as to why a particular apartment did not have hot water, and cut plaster and other works to isolate the problem,” said Abraham. “With the Stiebel Eltron unit, you can simply go in, open the cupboard where the unit is and if it is faulty, simply replace it, with absolutely minimal disruption to any built infrastructure or other people.”

According to Guss, Stiebel Eltron hot water units are MacCormack Consultants’ preferred hot water design solution for large unit developments. “We are working on several projects at the moment and, where appropriate, we will be specifying Stiebel Eltron for them,” he added.

Hickory’s Abraham said that the company was able to achieve ‘practical completion’ for Vogue South Yarra on schedule in December 2011, which meant that all major works were completed, with only minor defects and minor incomplete works to be rectified. All apartments were able to be handed over to their new owners on time.

Fletcher believes the water heaters supplied for Vogue South Yarra were instrumental in meeting the various project milestones. “Our solution provided the best environmental performance possible with the smallest footprint,” he said. “Compared with gas-fired alternatives, instantaneous electric water heaters have better heating efficiencies and a greater freedom to be positioned exactly where needed - thereby reducing water wastage.”

Building companies, such as Hickory, continually weigh up the cost effectiveness and environmental performance of water heating technologies to determine the most appropriate option for new multidwelling residential blocks. By installing Stiebel Eltron hot water systems, Hickory was able to minimise equipment and installation costs, while delivering efficient, reliable and environmentally responsible hot water to the Vogue South Yarra apartments.