Delivering hot water more economically

Current Building Regulations require architects and building engineers to actively seek opportunities to reduce energy or to use renewables. Initially the main focus of these reductions concentrated on reducing energy consumption for space heating and cooling – with the inevitable result that the energy required for domestic hot water generation now represents an increased proportion of the current energy needs of a building. Any energy saving that can be realised on the hot water distribution will therefore have a larger proportional impact on the total energy reduction of a building than most other services. The conventional means of distributing hot water throughout a building is that of a flow and return system, whereby water is constantly circulated from the central hot water plant around a building, returning to the water heater for re-heating after it has cooled in the distribution pipe. It is a classic example of pragmatic engineering design, albeit with an increasingly complex range of valves and controls aimed at achieving a hydraulic balance across the pipe network. The main design criterion of the flow and return solution is simply the temperature of the water at the tap outlet, with no consideration of energy efficiency. In fact the simplest synopsis of the re-circulation system is that it is actually designed to lose heat. All this is in contrast to more modern solutions – specifically electrically traceheated single pipe distribution systems. The trace heating solution addresses the central need of a hot water distribution system, i.e. that the water temperature is delivered at the desired level at every outlet, while also reducing the overall energy requirement for doing so. The result is a system that has as much as 50% less pipework, delivering quality hot water to every outlet. Significantly, this is achieved reliably at all outlets regardless of whether they are on the main distribution circuit, or on lengths of pipe known as deadlegs (i.e. lengths that would not even have been re-circulated on the old flow and return system). The HWAT system Tyco’s Raychem HWAT system is specifically designed for this application. The energy spent on warm water distribution can be reduced by 60% when compared with the energy a conventional recirculation system requires, while a significant CO2 reduction is achievable if the electricity powering the system utilises ecological energy sources, such as photovoltaics, combined heat and power, and other non-grid supplied sources. (If incoming electrical power is from the National Grid Tyco says the electricity consumption is carbon-neutral). Hot water temperature maintenance is achieved by attaching self-regulating heating cable along the hot water pipes to compensate for heat losses. Water temperatures can be maintained at any selected temperature up to that of the hot water services flow temperature, typically 55-65°C in “standard maintain” mode, with setback temperatures down to 45°C, and boosted temperatures to 70°C, for Legionella prevention cycles. The self-regulating heating cable continually adjusts its heat output at all points along its length in direct response to the “local” varying heat loss conditions at all points throughout the pipe network. Any given section of pipe therefore only receives additional heat from the HWAT cable where needed, and at a power output just sufficient to maintain the selected temperature. In this way hot water is always available instantly when taps are opened, avoiding water being wasted waiting for it to run hot. While hot water is flowing, the HWAT system’s thermal output is reduced, and, the more the hot water taps are used, the less the temperature maintenance system needs to be activated.

Programmable controller

The system utilises the HWAT-ECO controller, an easily programmable temperature control device that monitors the boiler temperature and ensures maximum efficiency of the whole system by incorporating setback temperatures for times of low usage. In this way power consumption is reduced to a minimum. As with recirculation systems, minimising heat losses via good thermal insulation is an essential element in lowering operating costs. The advantages of hot water temperature maintenance to a single pipe system should be particularly noticeable in large buildings like hospitals, schools, hotels, and commercial premises, where a significant proportion of the overall energy consumed is in the provision of hot water services across many tapping points. In addition to energy efficiency, the HWAT system also provides space, material, and installation time/cost savings, and reduces water wastage. Reasons for energy savings The energy savings can be attributed to a number of factors: