![]() ![]() In particular, leading designers should give more attention to:-selection of a representative external temperature for heat loss calculations-allowance for building exposure-suitable heat loss calculators, conforming to stated rules-refined intermittency factors, perhaps using the advanced method set out in BS EN 12831:2003-evaluation of emitter responsiveness, especially for emitters with fans-temperature-limiting controls, and modulation by reference to an upper temperature limit. Some of these have not been fully resolved. Instead of simply gathering information on current practice, the authors found it necessary to engage in extensive debate about many of the technical parameters governing system sizing, configuration and selection of components. It became apparent during the preparation of this guide that there is no generally well-established and understood design method for low-temperature domestic heating systems. This BRE Trust Report is aimed as a guide for those who wish to install low-temperature heating systems in dwellings, and concentrates on the calculations and other conditions necessary to ensure that low-temperature operation can be achieved. There is growing interest in low-temperature hydronic central heating systems, ie those where water is used as the medium to distribute heat around the building, and in which the water leaving the heat generator is limited to a lower temperature than in normal system design. Additional features such as zone heating thermostats and thermostatic radiator valves increase the efficiency of these systems.Low-temperature systems can improve energy efficiency and hence reduce fuel consumption and CO2 emissions. All radiators tee off the core pipes in the same size pipe work. The core flow and return pipes are sized depending on how far the water has to travel. The radiators use valves to balance them, depending on flow position, ensuring all radiators heat up. These tap into larger core central heating flow and return. The two pipe system provides each radiator with a flow and return pipe. This lead to the creation of two pipe systems that we use today. No matter what you do to reduce heat loss, or improve circulation, a large one pipe system will have excessive temperature differences. ![]() But for larger systems this is a one pipes Achilles heel. On a small system this can be minor, especially if all pipe work is insulated and the pipe run doesn’t have many bends in it. This system worked much better, however there were still drawbacks. By doing so, it would force more hot water to the farthest radiator before the water lost too much heat. The closer the radiator position to the boiler the greater the restriction setting of the radiator valves. With the use of radiator valves, they could balance each radiator, depending on what point of the system it received the hot water. Instead of the water running through one radiator to the next, a bypass provides the pumped water with two pathways. The one pipe system improved with the addition of a bypass on each radiator. This inevitably lead to a very unbalanced system, where the radiators nearest the boiler would be extremely hot and the final radiators on the system tepid at best. Early examples of this required much larger bore pipe work at the start of the system to ensure that the last radiators received some heat. A one pipe system sends the pumped water to each radiator in turn, and returns the water from the last radiator on the run. The water heats up inside and pumped to the radiators. So, why did we do it? Well, The original pipe work ran in a one pipe system and is not suitable for modern sealed systems. This is unusual because replacement central heating jobs can, in the majority of cases, use existing pipe work, providing it is in fit condition. In a new build or renovation this is fairly common practice, but this job replaced the existing heating system. We recently completed a full central heating project which included radiator pipe work. ![]()
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