Mark Ferris, Specificaon Manager at ELCO Heang Soluons, considers the water heang market and the dierent approaches to meet individual applicaon requirements.


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IT’S ALL IN THE PLANNING Hot water generaon the indirect way

s heating and hot water systems continue to evolve, the challenge for system designers is to adhere to the latest

efficiency targets, while ensuring commercial plant rooms retain their absolute performance. Indeed, performance is key – and no more so than when specifying equipment for generating domestic (potable) hot water (DHW).

So, what are the best options for consultants when specifying bulk hot water delivery? The first consideration is the level of demand for hot water, which can be split into three main categories: continuous demand, short heavy peaks, which often occur in sports clubs and leisure centres, and intermittent peaks (hotels or schools). One tried and tested method for bulk hot water delivery, which is ideal for continuous and intermittent peaks, is using gas-fired instantaneous hot water generators. These provide extremely high volumes of DHW and, thanks to their integral condensing boiler technology, allow for consistently high efficiencies. However, at typical hot water storage temperatures, the risk of scale fouling has to be considered. A unit’s performance can be affected by only a thin layer of scale, which can lead to heat exchanger failure. To alleviate the risk of such an eventuality, one option is to use an indirect unit – preferably with a stainless steel heat exchanger – which doesn’t suffer from these problems, due to complete hydraulic separation between the primary heat exchanger and the tap water.

Storage vessel

uTrigonXL features an advanced premixburner system for reliable performance.

Fully condensing units with built in storage are also capable of providing volume hot water delivery for peaks of usage, as well as producing near instantaneously heated water – even when the vessel is temporarily depleted. Furthermore, by incorporating the

storage vessel into the water heater and eliminating long runs of pipework – often associated with a boiler and an indirect cylinder – any heat losses from the primary circuit are kept to a minimum. In addition, an inbuilt close coupled plate type heat exchanger can help ensure maximum transfer of heat to the secondary circuit.

Certain gas condensing storage units also use the principle of loading the storage vessel from the top down with a very wide temperature rise. This allows for near fully instantaneous performance and optimises the efficiency as the feed water is picked from the lowest point in the storage vessel where the water is always the coolest at any given moment. Such a setup ensures units work in condensing mode for the vast majority of their operating cycles.

An alternative product of choice for providing larger volumes is a direct gas condensing water heater with a high recovery rate. This can satisfy the most demanding applications, while water heating units with high gross efficiencies are also able to complete the task effectively all year round.

Now, as mentioned, it is important to consider the potential for scale fouling in all cases, so the flow rate must be carefully regulated to alleviate any such issues. Furthermore, it is essential to specify units that have been manufactured to the highest standards, with the internal componentry and unit design a key consideration for any specification.

Premix burner system

Take the new TRIGON XL WH from ELCO as an example; this unit has been specially designed for the water heating market and, consequently, is suitable for commercial applications that require large quantities of hot water.

The main reasons for its suitability rest in its design, which features an advanced premix-burner system for reliable performance, a water-cooled

combustion chamber for the highest possible thermal conductivity, and optimised combustion zones for low emissions. These features, combined with a high grade stainless steel heat exchanger, result in unbeatable hot water performance.

There are a number of practical considerations when specifying larger water heaters, including the footprint and ease of servicing. The space a unit occupies in a plant room should be as small as possible for the output required, so consider water heaters that maximise their design by offering impressive performance from a compact unit. Plus, maintenance and servicing is always going to be an important element for any commercial building, so access around a unit – and to its key components – should be considered as part of the specification.

Annual usage

When it comes to hot water in larger properties, such as hotels, there are more instances where combined heat and power (CHP) units are utilised, which highlights some unique considerations – particularly the sizing of CHP unit and the accompanying thermal store. This requires an hour-by- hour operating model to be constructed to represent the annual usage of a building’s needs; everything from the number of predicted showers and baths, to meal preparation and washing machine cycles should be included, to ensure CO2 emissions savings are optimised. Providing powerful hot water production in commercial buildings is a complex task and one that requires careful consideration. Part of this process should involve consulting manufacturers of the original hot water equipment, as they have a wealth of knowledge and expertise on hand, so specifiers can seek their help from the outset.

Of course, there is not one sole product or system to suit every building’s needs. However, with careful planning and real consideration of the factors outlined, it’s easy to ensure that DHW can be delivered effectively, while keeping energy usage to a minimum. 10 BUILDING SERVICES & ENVIRONMENTAL ENGINEER DECEMBER 2017 VISIT OUR WEBSITE:

uThe TRIGON XL WH from ELCO is suitable for commercial applicaons that require large quanes of hot water.

One tried and

tested method for bulk hot water delivery, which is ideal for connuous and intermient peaks, is using gasfired instantaneous hot water generators. These provide extremely high volumes of DHW and, thanks to their integral condensing boiler technology, allow for consistently high eciencies.

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