Indirect Water Heating For Public Sector Projects
Indirect-fired water heaters (also known as calorifiers) and buffer tanks are a requirement on public sector build projects where large volume storage of water at high temperatures is specified.
To introduce thermal energy an additional heat source is required. Typically, the water will be heated directly by a gas or preferably an electric boiler, passing it through the cylinder and using heat exchange to transfer energy to the cold water in a separate system of pipework. This does mean that an indirect water heater cannot react as quickly to demand as a direct-fired water heater, however, with the cylinder working as a buffer and storing the hot water it reduces the operational demands placed on the boiler. With the boiler no longer required to work as hard to meet the domestic hot water (DHW) needs of a building, energy is saved, costs are reduced and emissions fall.
Due to the transfer of heat through the walls of the heat exchanger element, the two fluids do not mix. This allows for more options in terms of the external heat supply and introduces a range of renewable technologies that use other fluids for heat transfer including solar thermal collectors and Air Source Heat Pumps (ASHP). Using heat pumps or solar as an energy source to preheat water within an indirect cylinder then enables a reduction in work from the direct top-up heat source. This is what enables DHW systems to reduce energy costs and emissions to varying degrees depending on whether this additional heating is provided by electricity or gas.
One other key advantage of separating the supplies is that the risks of external contamination such as a build-up of scale in hard water areas or the corrosive effects of soft water are curtailed.
As with any hot water application, understanding the relationship between storage and recovery, and correct sizing is extremely important for efficient and cost-effective operation. The patterns of hot water usage and recognition of periods of peak demands often make sizing a complicated process, with many systems overcompensating and, by being oversized becoming more costly and less efficient. At its simplest, a commercial system should hold an hour of hot water output in storage, but the function of the building, its population and activities will adjust requirements, for example, where hospitals will typically exhibit a 24/7 demand for hot water, schools and offices may be limited to just 7½ hours per day. In some refurbishment scenarios, we will also see a physical limitation of space available for DHW storage, in which case a system will put more demand on the boiler or renewable to increase the output for preheating, reducing the required size of the cylinder.
Integrating an indirect water heater within a hot water system gives you a number of design options, as a larger cylinder means the boiler can be smaller, or the reverse if the existing system has a large efficient boiler. Understanding the hot water demand is critical. If demand is not so great, then using a larger cylinder can lead to unnecessary capital and ongoing operational expenditure. Go too small and the storage could prove inadequate and the system will not achieve its operational requirements. Attaining the correct balance of demand and efficient, cost-effective supply is what ultimately defines a successful system.
At Adveco, these factors are supported by a wide variety of cylinders. The Stainless Steel Indirect (SSI) range, for example, is supplied with a single high-output internal heat exchange coil at a low level to serve as an indirect water heater.
The ATSx range provides water heaters designed to be used with indirect heat sources across a range of DHW installations exhibiting smaller demands but requiring more than six bar pressure. For more complex and renewable-based systems, the Stainless Steel Twin-Coil (SST) or ATSR ranges offer a pair of independent internal heat exchange coils to serve DHW systems. Each high-output coil can be used with a separate heat source, enabling effective integration of renewable technologies or multiple heat sources, or alternatively can be combined to increase the heat transfer capacity from a single high-output source.
The GL range of hot water cylinders provides a lower cost choice, with the GLC serving as indirect water heaters or preheat vessels, GLE serving as an electric water heater or buffer, and the GLT range offering twin coils for two separate heat sources.
These hot water cylinder ranges come with multiple connectivity options and offer from 200 to 5000 litres of storage, giving specifiers a wealth of choices when designing bespoke DHW systems with Adveco.
