51 HPM 0214

HPM February 2014

WWW.HPMMAG.COM Got a story? Ring us on 01732 748041 or e-mail twood@unity-media.com WATERHEATING,TANKS&CYLINDERS Continuous flow versus heat and flow Chris Goggin, associate director/operations at Rinnai, examines two options available when choosing a hot water stored system... Rinnai’s Infinity condensing unit HEATING & PLUMBING MONTHLY FEBRUARY 2014 51 Switching from a hot water stored system to a continuous flow one can save hundreds and thousands of pounds a year, according to recent comparisons. Stored hot water, by virtue of their system design, can find it difficult to cope with present day demand, as the recovery times are more often than not longer than the period of use. The length of time this type of product has been on the market - plus clever and effective marketing - has ensured that people think hot water storage systems are a cheaper option and do more than they actually do. End users, installers, contractors and specifiers need to take a longer view. If they take the time to compare actual base running costs for a continuous flow system all day every day, like for like, with those for a stored system, they will find they can save between 25-30% in energy bills over the lifetime of that appliance. The only time you are paying for energy use is when there is a demand - in other words the system will only burn gas when a tap or shower is being run. INITIAL CAPITAL COST The end user should be considering what it actually costs to guarantee a store of hot water that has to be brought up to 65°C from cold and then maintained at that temperature 24/7 even when it is not being used. When all the water is used up, fresh cold water will be heated and then stored until it is needed meaning there could be up 24 hours of standing losses – 48 hours in a typical office block over the weekend. The figures just don’t add up. There is a responsibility as an industry to look beyond the initial capital cost and reviewing full life cycle costs. Stored hot water systems are almost always designed to over capacity because it is so difficult to calculate the amount of hot water needed -demand can change day-to-day. For example, how much store for peak loads? Estimated lengths of shower time per person? How many people? How much water? Will it be two litres per head? Or three? Or even maybe five? It is all guesswork so systems are oversized in compensation and they use too much gas and too much storage - wasted money. A Rinnai-funded study recently costed a project to replace a boiler and calorifier providing hot water only, no heating, for a school’s annexe kitchen. The kitchen was not in continual daily use and was shut over weekends. A continuous flow system would have been ideal in this situation because when no hot water was being drawn off, no gas would be used, therefore, no energy charges. Conversely, a traditional storage system, which would have to heat and store water until it is needed, incurs cost and wastes valuable resources. SUPERIOR UNITS Operated via a built-in digital controller, the water heater provides near mains pressure flow for as long as is needed. Burners on these superior units use lean and rich burner technology allowing them to self-modulate down to an unbeatable 2.2kW. In many commercial operations, these heaters are the best of all possible options. Multiple condensing units can be linked via a manifold arrangement to provide a never-ending supply of heated water without costly storage in the most demanding situations. The units are available in internal and external choices. There is no danger of scalding as the unit cleverly eliminates sudden changes in water temperature. The water temperature set via the digital temperature controller is the water temperature that is delivered. So, for example, in a domestic application, if somebody is showering at, say 42°C, and a tap is turned on elsewhere in the house, the temperature will not vary. As a failsafe, the unit will automatically cut the heater off should the temperature rise by 3°C above the chosen set point. The condensing process delivers up to 95% thermal efficiency, which translates to significant energy savings when compared to standard ondemand water heaters. The government itself has recognised the value of modern condensing technology in gas fired water heaters in its battle to meet its own targets to cut carbon emissions. It announced that from October 2013* the use of non-condensing gas fired water heaters will be eliminated in new build projects. End users and specifiers really must take into their calculations lifetime cost and choose a product with quality engineering that uses only the best components available and is precision engineered, technically advanced and up to the job it needs to perform. *New Building Regs proposals suggest that noncondensing gas water heaters cannot be employed from October 2013 in new build projects and industry experts are predicting this will extend to refurbishment and replacement. enquiry number 136 Rinnai’s Infinity HDC1200 condensing unit would give payback for a continuous flow system in a fraction over two years simply because of slashed running costs. The model illustrates that payback would be even sooner as in reality the system would actually use less gas. • Cost of Rinnai Equipment (confirmed) and Installation (assumed) £2,650 • Cost of replacement 15kW Condensing Boiler & Installation (assumed) £1,600 • Capital cost differential £1,050 • Usage of gas per hour assuming demand load of 320 litres per day for Continuous Flow System = 0.98 metres cubed • Usage of gas per hour assuming demand load of 320 litres per day for indirect storage via 15kW boiler System = 1.92 metres cubed Saving based on 38 week x five day load profile £520.60 per annum • Payback in 2.01 years based on steady load demand. If less water hot water required gas consumption for the Rinnai falls and the saving increases as the storage tank will be required at delivery temperature irrespective of demand. Payback period will improve significantly if load demand falls.


HPM February 2014
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