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www.heatingandventilating.net


Specifying for DHW


Ensuring efficient hot water delivery in commercial buildings can be a challenge. Andreea Manoiu, solutions centre manager (pictured left) at Elco Heating Solutions, outlines the approaches available


F


ulfilling the requirements of high hot water demand has its challenges in a range of commercial applications. From large residential apartment blocks in cities, to hotels and leisure centres, all properties will have their own specific needs, with different products and system designs more suitable than others. The main reason buildings differ so widely in their hot water needs is due to a combination of peak flow rate, predicted demand and the usage patterns. Taking these three factors into account is essential in designing an effective system, regardless of the size and scale of a project, as the equipment specified will need to deliver enough hot water during a building’s busiest periods. If a school is taken as an example, it is fairly easy to predict the patterns that will occur day to day, as this type of property usually has set opening and closing times, as well as a schedule of activity that takes place throughout the week. However, when considering the hot water demands in an application such as a leisure centre, the


daily routine can be very different. Although there is likely to be a timetable for opening and closing (although the latest gyms are more frequently open 24/7), DHW demand can vary from day to day, depending on the number of gym goers. So, a worst case scenario needs to be assessed for a fully occupied centre when every visitor takes a shower, how often peak delivery is repeated during a day, and the average continuous DHW demand throughout a 24-hour period. These factors combined will help create a demand profile of the building. Of course, the easiest way to narrow down the options for products that cope with peak demand is to look at any existing or estimated patterns of usage, although this task shouldn’t be taken lightly. If the system is under-sized, it could result in a shortfall of hot water being available for the building’s occupants. Conversely, oversizing a system can cause a vast amount of energy to be wasted, which isn’t an option in an industry where energy efficiency is of the utmost importance.


Direct or indirect?


There are two distinctive appliance types for hot water delivery: direct and indirect. Each approach has its own benefits and drawbacks to, depending on the type of commercial building in which they are to be installed. A direct unit has an integral heat generator, e.g. a gas burner, which directly heats the water flowing through it, offering some unique benefits, including rapid response times and reduced potential for heat losses in pipework, such as that between a boiler and calorifier, for example. Plus, the latest direct-fired gas water heaters are condensing appliances, incorporating a room sealed pre-mix combustion system, ensuring latent energy (present in water vapour discharged through the flue) is recovered and not lost to the atmosphere. This helps deliver higher gross thermal efficiencies of up to 96%. In addition, condensing water heaters considerably reduce NOx emissions, making them suitable for new build properties. Some products, such as Elco’s new Tudor NHREC, will transfer heat into a stored volume of water that surrounds the firing tube, whereas other direct products will utilise a heat exchanger to the point of use – which leads to the next consideration.


Instantaneous or instantaneous with storage?


In order to deliver DHW to the point of use, there are a couple of different approaches. The first is an instantaneous mechanism, which heats the water as it is delivered to the point of use. In practical terms, a good commercial example is a leisure centre with a swimming pool that needs to maintain a set temperature. In this scenario, the water is often heated directly and transferred straight to the point of use, which requires a direct fired unit, such as the TRIGON XL Water Heater (model ZW). These types of instantaneous units are specially designed for swimming pools and can be highly effective, delivering a large volume of DHW per hour.


An alternative, and potentially more cost effective approach, is to use a combination of instantaneous DHW generation alongside a stored volume that is held at a set-point temperature. This will satisfy the requirement for high volume delivery over a short period of time, by using both the stored volume of DHW and a proportion generated by the instantaneous hot water heater. Delivering bulk hot water in commercial buildings, while maintaining high efficiencies is not a simple task. It’s clear that instantaneous gas-fired hot water generators still have an important role to play, but it is crucial to assess a building’s peak demand and patterns of usage to ensure the chosen approach remains effective in the long term.


Elco’s Trigon XL water heater


Water heating


www.heatingandventilating.net


April 2021


15


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