BSEE BOILERS & HOT WATER


open if they have no hot water. When replacing an old system, you currently have several options available:


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By Kevin Poer, Business Development Manager for Hot Water Soluons at Hamworthy Heang.


u Replace like for like with an atmospheric water heater u Upgrade to a condensing water heater u Switch to an indirect calorifier heated by a boiler or plate heat exchanger heated by a boiler u De-centralise and install point of use water heaters


From 26th September this year, your options might change. Why? The Energy-related Products Directive (ErP) introduces new minimum energy efficiencies and NOx emission limits which will affect many atmospheric water heaters.


Before these changes come into force, we recommend taking a look at the current hot water system earlier rather than later in order not to be caught out by legislation and more limited product choice.


Considering project specifics


Which hot water system best serves my purpose? This depends on the quantity of hot water needed which will differ vastly when comparing a leisure centre, for example, to a church or office building. While the leisure centre will have a high hot water demand owing to shower use of many individuals throughout the day, the office may only have a low constant demand from basins and kitchens. Each will have a different demand profile and require different “minimum safety levels” in order not to run out of hot water.


Modifying flues


uCalorifiers heated by boilers with a high turndown rao can eecvely reduce gas consumpon. The combinaon of indirect fired water heaters and modular boilers has achieved gas savings of almost 40% at St Paul’s Cathedral.


If changing from atmospheric to condensing water heaters, a full flue system change is required. This is not only to enable the flues to deal with the slightly acidic condensate from the flue gases but also with the positive pressure created by the fan assisted burner.


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ARE YOU PREPARED FOR NEW LEGISLATION? How change could aect your water heater choice


reliable hot water supply is vital. Many buildings, such as government


premises, hospitals, and schools cannot


If atmospheric water heaters and atmospheric boilers are on a combined flue, there is more to consider. In case the water heaters are being upgraded to condensing models, the flue system will need to be separated, as condensing appliances cannot be combined on the same flue as the atmospheric models.


If separating the two appliance groups is not possible due to space and budget constraints and possible flue runs, an indirect fired water heater can be an option if sufficient boiler capacity is available. If not, a replacement of both the boiler and water heaters to highly efficient condensing models for greater efficiency and energy saving gains is a viable alternative.


Dealing with condensate


It is not just the flues that need to be considered when dealing with flue gases of condensing equipment but also the amount of condensate from the water heaters. When operating at suitable condensing temperatures, a condensing water heater has the potential to produce condensate at up to 13 litres per hour per 100kW input energy. A condensate pipe will be required from the water heaters to a suitable drain. If there isn’t an accessible drainage point, for instance in a basement plant room, a pump can be used to pump the condensate to a drain, possibly at a higher level.


Considering a calorifier as a costeecve opon


We‘ve looked at the challenges the installation of a condensing water heater can present. Considering this, changing to an indirect fired water heater looks like a favourable option: no flues needed, no condensate to get rid of, cheaper, easy to install and can be just as efficient as a condensing water heater.


However, if using an existing boiler, the heating circuit needs to be broken into which can mean disruption to service in the building. The existing boilers might not have the capacity to provide additional heat for hot water. In this case, additional or new boilers may be necessary, including extra pumps and possibly controls to prioritise hot water over heating. However, some modern boilers already have built-in controls which can do this.


Eciencies and separaon


How can efficiencies from different heating system components be best achieved? This is not only a question of how they interact with each other but also how individual products are set up to reach their full energy efficiency potential. Higher boiler temperatures are for example necessary to heat a calorifier. For a condensing boiler to be working most efficiently, it should operate with low return temperatures to provide


greater opportunities to condense and run in its most efficient state. The ratio of hot water demand to heating is a key consideration. During the summer months, demand for heating will be low. That’s why a large boiler can be oversized when it’s only delivering heat to a calorifier. However, modern boilers can counteract this. Due to their ability to adjust the output (modulate) to lower requirements, e.g. a 5:1 turndown, they do not need to work flat out at full capacity. This way, the boiler can operate at e.g. 20% to meet the hot water demand in the summer. When heating demand returns in the autumn/winter, it can then modulate up incrementally to full capacity. On the other hand, by separating heating and hot water with the use of standalone direct fired water heating units, it is possible to raise the efficiency of the hot water generation, particularly in summer. Another benefit is the ability to have separate control of both systems. There may be higher costs for the installation and maintenance associated with direct fired water heating units.


However, many premises cannot risk a combined system as they need the assurance and backup of the heating and hot water systems operating independently. Hospitals or prisons for example typically design their systems with 100% redundancy and we generally see them opting for direct fired units. This gives them the best security in supply for safety of their building occupants.


Bringing it all together


With so many details to consider, we always recommend starting with the client’s key objectives – security of supply, efficiency, cost. Next step is to evaluate these in relation to the site, as well as hot water demand and the practicalities of the existing space (plant room) and equipment (boilers and flues). Given that there are many factors to take into account, the planning and design stage will take longer. Therefore, enough time should be allocated to ensure key objectives of the customer are met.


www.hamworthy-heating.com 18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JULY 2018 VISIT OUR WEBSITE: www.bsee.co.uk


uDepending on hot water and project requirements, calorifiers (le) or direct fired water heaters (right) can be a suitable choice.


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How can


eciencies from dierent heang system


components be best achieved? This is not only a queson of how they interact with each other but also how individual products are set up to reach their full energy eciency potenal.


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