056 HPM 1012

HPM October 2012

TRAINING/TECHNICAL WWW.HPMMAG.COM Got a story? Ring us on 01732 748041 or e-mail twood@unity-media.com Renewables an option for towel rails Nu-Heat’s technical director, Andrew Grimsley, looks at a practical way for a towel rail to be integrated with a heat pump system... Tbathrooms, it is advisable to have a towelhe Domestic Building ServicesCompliance Guide says that whereunderfloor heating (UFH) is used with rail. The reasoning behind this is that the useable floor area of a bathroom for UFH is generally small in relation to the room size, and the UFH may not provide enough warmth for the room on its own, so towel rails are suggested as a heating supplement. Secondly, an en-suite bathroom may share the bedroom thermostat, meaning that if the temperature is turned down for the bedroom, the bathroom will also get cooler (the choice of a separate ‘stat is always given to the customer). The main issue with towel rails on a renewable Towel rails can be used on system is that they may be required to be on a renewables system such throughout the year, not just during the heating as a heat pump season. With a heat pump the main system will be weather compensated, so that as the outside bacteria. is still a more efficient method of heating towel temperature increases the heating flow Nu-Heat’s solution to the temperature issue is rails than electricity, the only other alternative for temperature gets lower, until a point is reached to use the coil in the cylinder that transfers heat a heat pump system. Electric towel rails have, in where no heating is required. into the DHW to transfer it back out and around essence, a CoP of one, where a heat pump In this case, although a towel rail will be the separate towel rail circuit. supplying the DHW and feeding the towel rails heated sufficiently when the weather is cold, the To achieve this, control of the system must be will still achieve a CoP or two–2.5, meaning that heat pump’s weather compensation means that carefully considered. If the towel rail is being this system will be greener and cheaper than the in warmer weather, the water available for the heated while the cylinder is warming up, it will electric alternative. towel rail will not be hot enough. take too long to reach the required temperature, Another bonus is that any type of towel rail possibly starving the main heating system. can be used, not only the non-ferrous or stainless DOMESTIC HOT WATER LOOP Therefore, the coil should either be connected steel towel rails required for a hot water-fed loop. With a boiler system, the towel rails can be on a to the heating or the towel rail – not both at the Additionally, unlike rails on the hot water loop secondary domestic hot water loop and heat can same time. This is achieved relatively simply that will run at a constant temperature, be requested from the boiler instantaneously at through the use of valves. This solution achieves thermostatic valves can be installed into the the required temperature throughout the year something that would otherwise be fairly system, both protecting the temperature of the (via the hot water cylinder). difficult to implement. towel rail from the perspective of safety and Unfortunately, the same principle cannot be However, when a heat pump is used for preventing overheating of the room temperature. applied to a heat pump system. This is because heating, it reaches its best Coefficient of Benefits of system: heat pumps produce lower water temperatures Performance (CoP), partially due to the weather • Control; as the towel rail circuit is a separate than boilers, so there is a danger of Legionella compensation, but when it is used for DHW the circuit, timing and temperature can be proliferation and the risk of Legionnaires’ CoP is not so high. In order to offset this and controlled independently disease. keep running costs down, the towel rail needs to • Thermostatic radiator valves can also be used Boiler-heated water is stored at 65°C in, for be timed so that it is only used when required. for independent control (not possible when example, an EnergyMaster thermal store, and this Even with a reduction in the achievable CoP, it the towel rail is on the hot water loop). is the temperature which will be transferred to the domestic hot water to flow out to the hot water loop. The return temperature will therefore LEGIONNAIRES’ DISEASE – A REMINDER be around 55°C with towel rails. As Legionella cannot survive above 48°C, there is no risk of Legionnaires’ disease is a form widespread in natural water purpose-built systems where the bacteria multiplying in the water. of pneumonia resulting in systems like rivers and ponds, water is maintained at a In a renewables system, although there is flu-like symptoms such as but do not tend to transmit to temperature high enough to enough heat for the towel rail in the domestic high temperatures, fever and humans from these sources. encourage growth, including hot water (DHW) that is heated constantly to chills, cough, muscle pains Instead, most outbreaks hot water systems used in just above 50°C, the temperature returning to and headaches. occur from exposure to offices and homes. the cylinder from the towel rail will be too low, Legionella bacteria is Legionella growing in leading to a potential breeding climate for the 56 OCTOBER 2012 HEATING & PLUMBING MONTHLY enquiry number 140


HPM October 2012
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