Energy efficiency


Try it on for size


W


hen it comes to sizing hot water heaters, how times have changed. The availability of online tools has made manual calculations


a thing of the past, and there is now a much wider range of products to suit a greater variety of user requirements. What’s more, energy efficiency is higher on the agenda and legislation is constantly evolving.


When it comes to sizing water heaters, striking the balance between output and efficiency is critical. Oversized systems are problematic in many ways, as the capital outlay is greater on larger plant; more energy is used in operation; and, even if the demand for hot water is not there, the end user will end up with more expensive bills. It’s also worth noting that larger plant takes up more room, and can therefore be more difficult to install if there is only a limited area available for siting equipment. Thankfully, by following these simple steps, this scenario can be avoided.


Building type and usage


A recommended starting point is to consider the type of building and its usage, as this will impact the demand. For example, the peak periods in a hotel may be considerably different to a nursing home and, as such, require a different approach. Most hotels experience an uptake in water consumption between 7-10am and 4-7pm when guests are preparing for their evening out. Conversely, residents in a nursing home are more likely to use washing facilities throughout the day, depending on when care staff are on shift. On a retrofit job, where the water heater will fit into the existing heating system is an important factor. Will it be the primary heating product, or will it supplement other technology such as combined heat and power (CHP)? Some models, such as COMBIflo even have space heating capabilities, so it makes sense to factor this into product selection.


Outlets, peak periods, and capacity


The next step is to establish the number of demand points, outlet temperature, required flow rates, basin capacity, length of the peak period and number of


36 November 2017 The type of water heater is also a consideration


here: is the building supplied by natural gas or does it use LPG? Does the customer want a condensing or non-condensing model? The latter is usually a no- brainer, as condensing water heaters offer better energy performance, providing the customer with more manageable running costs.


Storage and recovery


Finally, recovery rates and built-in storage should be taken into account.


When only a small amount of hot water is needed each time, in-built storage in a direct-fired gas water heater can often enable this to be supplied without firing up the water heater. Stored water also provides the initial supply of hot water when demand is high. However, if peak periods are close together, we would, depending on the time between them, recommend to size for a water heater with recovery in mind only. The Size-it tool from Andrews Water Heaters guides users through these key stages with ease. It takes all the supplied information and performs the complex calculations – removing the burden from the specifier. It also provides quick access to information on legislation such as ErP or Part L


Size-it is Andrews Water Heaters’ original sizing tool for water heater specification


What parameters should specifiers consider when selecting the best water heaters for the job? Dan Martindale, sales director at Andrews Water Heaters, goes through the simple steps to perfect sizing every time


fills during this time. All of these factors dictate the size and type of water heater best suited to job. For customer satisfaction, it is imperative that the products installed are powerful enough to achieve the desired flow rate and temperature – otherwise the customer will complain that their new equipment ‘doesn’t work’.


Type and quantity of water heaters


After this, specifiers should consider how many units the customer wishes to have. In commercial applications where hot water supply is business- critical, such as a hotel, we would recommend installing more than one water heater. Compared with one piece of equipment with a higher output, multiple units ensure a level of continuity of supply. Of course, the amount of plant space available would also dictate the quantity of units a building can accommodate.


Building Regulations. By using it, users can earn two credits to increase the water heater’s efficiency value entered into an approved National Calculation Methodology tool. More complex projects are referred to an Andrews Water Heaters area sales manager (ASM) for in-depth advice and consultancy. Sizing water heaters can be a subjective task, but with a little assistance the process can be made much more straightforward. * When assessing the expected performance of water heaters for compliance with Building Regulations Approved Document L an additional 2% heat efficiency credit is given for the use of manufacturers’ water-heater sizing guides.


Andrews Water Heaters Supaflo Condensing Water Heaters


www.heatingandventilating.net


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