Heat pumps
Heat pumps & fan convectors a match made in heaven?
Jim Bennett questions the conventional wisdom that, when using heat pumps, underfloor heating should be specified for new build projects, while for renovations and upper floor in commercial buildings, the existing radiator footprint should merely be resized
Left:
Smith's Fan Convector diagram - how it works
Above:
Smith's Caspian Universal (Model 90 series)
mounted, or under a kitchen base unit, depending on the project and commercial needs of the building they are working on.
thinking com- pletely overlooks the technology inherent in air or ground heat pumps, which have been designed to work at optimum tem- peratures around 40 °C. While underfloor heating does perform well using this sort of temperature feed, panel radiators struggle to produce natural convection at this sort of heat load. In comparison, a fan convector, which is plumbed in to operate from the boiler in the same way that a panel radiator would be, can function efficiently and effectively at these much lower water temperatures. Fan convectors use forced-air convection, via a small energy-effi- cient electric fan. They circulate heat, generated from either a boil- er or heat pump, quickly into the living or working spaces providing effective heat, almost instanta- neously. When the room tempera- ture reaches the set temperature, it will switch off. Once the room drops below the set temperature, the fan convector will switch itself back on. Typically, a standard radi- ator is much slower to heat up, less responsive especially at lower temperatures, and loses around 10 per cent of its heat to the wall it is sitting on.
34 | October 2014 | HVR
Heat pumps, by design, work at their optimum efficiency at much lower temperatures than a con- densing boiler, typically around 40°C. To pair a radiator with a heat pump seems to be a peculiar step to take, given that the typical radiator, by design, is more effec- tive at high water temperatures, and loses most of its impact at temperatures lower than 55°C. Yet the prevailing advice is, that to overcome the challenge of these lower temperatures, the radiator needs to be considerably larger, in order to provide the required heat for the space available.
In contrast, fan convectors can have much smaller footprints than the equivalent output radiator, when paired with heat pumps. A hydronic fan convector is capable of distributing heat efficiently and effectively, irrespective of the input water temperature. In fact, the larger the radiator, the bigger the difference in footprint (wall space) between a fan convector and a radiator. Unlike a panel radiator, fan convectors are immensely flexible in terms of how and where they can be sited, giving specifiers the option of placing them high on walls, embedded in ceilings, floor-
Commercial installers and specifiers alike should take into consideration the merits of fan convectors, when heat pumps are part of the equation for heating either a new build or renovated commercial space. They should certainly pause for thought when comparing SAP calculations between radiators and fan convec- tors. As an example, a SAP calcu- lation using the combination of air source heat pump and fan con- vector in a new build property, should show at least a 12 per cent reduction in running costs, which is close to the efficiencies achieved by installing under floor heating. Fan convectors also only use five per cent of the water content of an equivalent output radiator, ensuring that they are more responsive to ever-changing daily weather patterns, as well as people’s personal heat preferences.
It may also be useful for installers, especially on light commercial installations, such as in places of worship or schools, to also take note of the MCS website: http://www.microgenerationcerti-
fication.org/mcs-standards/inst- aller-standards.
Here, they will find the down- loadable document MCS 021 heat emitter guide which provides all
the information required to match heat emitters with the heat pump they are installing. The guide has been put together by the Department of Energy and Climate Change, with input from a wealth of esteemed industry bodies, such as the Energy Saving Trust (EST), the Heat Pump Association (HPA), and the Institute of Domestic Heating and Environmental Engineers (IDHEE). In the Foreword, it very clearly states that the performance of heat pumps will be at an optimum if installers choose to use low-tem- perature heat emitters to transmit heat around the [premises]. It says, ‘A fan-assisted radiator (fan con- vector) will have a higher heat output than a standard radiator the same size. You can therefore achieve a higher Temperature Star Rating without the heat emitter becoming too large for a room with a fixed specific heat loss.’ Fan convectors do not immedi- ately come to mind when specify- ing heat emitters; however they should be on every heat pump manufacturer’s radar, when advis- ing their client base on how to obtain the optimum performance from their products. Equally, astute commercial specifiers and installers will always be interested in learning about alternative solu- tions for heating projects they are involved with. At Smith’s, for example, we find that once our clients have used fan convectors for particular types of project, they rarely go back to other forms of heating, when presented with sim- ilar project challenges. Modern fan convectors are quiet, easy to install and provide installers with a strong means of providing a system that allows the heat pump to operate close to its maximum efficiency, to achieve enhanced running cost savings and carbon reduction. From this perspective, heat pumps and fan convectors certainly do seem to be a match made in heaven.
// The author is the sales & marketing director at Smith’s Fan Convectors //
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