‘As the Government gets firmly behind renewable energy with the confirmation of the Renewable Heat Incentive, installers need to look at the options available for making the most of these ‘green’ technologies,’ Adrian Troop, Nu-Heat’s Sales & Marketing Director.

Options

Renewable energy encompasses any technology that takes its energy from the natural resources of the sun, wind, tides and ground. ‘Renewable’ simply means that this energy, unlike fossil fuels, is self-replenishing. There is an increasing range of renewable products, from wind turbines and wave hubs to biomass boilers, heat pumps, solar thermal and photovoltaic.

What has become increasingly apparent is that no single technology offers a complete solution, and that the way to achieve the most energy efficient systems for customers (and also to meet the increasing levels of the Code for Sustainable Homes) is in the integration of different technologies.

Heat pumps with underfloor heating

The low flow temperature of warm water underfloor heating makes it an ideal partner for heat pumps, both ground source and air source. When UFH is specifically designed to be fed by a heat pump, additional tubing and more efficient floor constructions facilitate the lower flow temperatures whilst still achieving the required internal temperature. Factors such as the thermal resistance of the floor covering are included in the heating calculations to determine the correct tube spacing. A floating floor panel with variable centres such as Nu-Heat’s Tri-Panel allows the most suitable tube density to be selected for appropriate flow rates, whilst screed offers the greatest flexibility and is arguably the best floor construction for conductivity.

Heat pumps with radiators

Conventional thinking has questioned the viability of heat pumps integrated with radiators from the simple fact that reducing the flow temperature from 75 to 50°C requires a standard radiator to be approximately 250% bigger than normal. However, high output, low temperature radiators such as Jaga Strada’s DBE range go some way to answering this issue. The Strada features low energy fans activated by an intelligent temperature monitoring function to boost output by precisely the right amount.

Heat pumps with underfloor and radiators

A combination of UFH downstairs and radiators upstairs may be a possible solution for a retrofit situation. Again, using the more energy efficient radiators available makes this a viable option. The goal of a combined UFH / radiator installation is to keep the UFH and radiator temperature exactly the same in order to maintain the efficiency of the heat pump system; low temperatures and a good Coefficient of Performance (CoP).

Sizing a heat pump

A system must be designed to deliver the best possible performance. Nu-Heat, for example, uses highly regarded design capabilities to ensure the correct sizing of a heat pump. Specialist software runs a simulation of performance over an average year, based on local monthly weather data. Heat pump systems are designed to an outside temperature of -3°C and an optimum bivalent point (the point at which supplementary heating cuts in). Once a heat pump has been sized, Nu-Heat calculates a year’s heating and hot water requirement giving an assessment of the Seasonal Performance Factor, including an estimate of the total heating and supplementary energy usage and an approximate cost for running the system.

Heat pumps, underfloor heating and solar thermal

Practical issues for heat pumps

Ideally the building heat loss should be 35 – 40W/m²

GSHP needs land approximately 2.5 the floor area of the property to lay the ground array

ASHP needs space outside for siting

Both heat pumps require an indoor area to house the system components

To help achieve an even more efficient system, solar thermal can be integrated into the design. For domestic hot water, a cylinder such as Nu-Heat’s EnergyMaster HP Solar 360L hot water tank with solar coil will be appropriate. Each element of an integrated system is supplied with its own product-specific control so attention must be paid to insuring that there is no conflict between the controls. Information about what times of the day the heating and hot water will be used helps with the correct programming of the heat pump and solar controllers, ensuring maximum efficiency from both. The underfloor heating can be set back to reduce building heat loss whilst not in use. When specifying an integrated system, it helps if the supplier knows the estimated water usage – the number of bathrooms, power showers and so on to allow correct sizing of the system.

In summary, to achieve the best energy efficient system for customers, accurate design is of paramount importance as is the necessity to ensure that all of the technologies have been configured to work together in one integrated system with control systems that complement each other by making the most of their individual operational characteristics.