Roundcroft - Air source heat pump case study

Roundcroft is a high spec’ new build home, built by Oaklyn Construction Ltd. One of the many innovations is the use of an Air Source Heat Pump (ASHP) for the central heating and hot water provision, linked to under-floor heating throughout the house.

---

The main heat source is an externally located Stiebel Eltron WPL 23 Air Source Heat Pump, located behind the original garage building.

---

All the associated controls, storage cylinders, etc. are located in a purpose built plant room within the original garage building.
The hot water storage cylinder and the central heating buffer cylinder are connected to the main house via a purpose made, highly insulated, multi core pipe duct, which runs below the ground from the original garage (now a studio building) on the left to the house via the utility room.

---

The heat pump is concealed from casual view behind fence panels

---

The system is what we call a bivalent system. This means that the heat pump does as much of the work as possible, but in times of high demand, or very cold weather, the additional heat required is provided by the lpg gas boiler located in the plant room.

The domestic hot water is provided from the large storage cylinder on the left and the water is circulated round the house on what we call a secondary circuit, by the yellow coloured pump to the left of the cylinder. This ensures almost instant hot water availability at all draw off points.

---

The system also has a buffer cylinder. This is a store of water heated by the heat pump, this has three main functions, it allows the heat pump to run as long as possible when operating, and reduces the cycling (switching rapidly on and off) of the heat pump. Secondly, it provides a cushion within the system for times of high demand, so there is a reservoir of heat that allows the heat pump time to catch up with demand (heat pumps are generally a little slower than boilers to get up to maximum temperature). Thirdly, because of the high flow of water through the heat pump, it allows for optimum efficiency and higher output temperatures from the heat pump.

---

The whole system is controlled by Stiebel Eltron’s own, purpose made, intelligent, optimising controller. This is designed to maximise the overall efficiency of the heat pump and the system it is connected to. The controller looks at the temperature within the house, the outside temperature and the buffer temperature.

---

It then runs the heat pump to achieve the correct water temperature within the buffer to provide a sufficient level of heat for the house. If the heat pump cannot achieve the required temperature, due to demand or very cold weather, the controller can top up the temperature of the buffer using the gas boiler.

---

Because heat pumps work most efficiently when the water within the heating system can be kept to a relatively low temperature, around 40 degrees Celsius, the system works best with low temperature heating emitters. In this case the whole house has under floor heating. The water is circulated from the buffer cylinder (3) via the multi core pipe work below the ground, to the distribution manifolds within the house. This allows for individual control of each room via the actuator heads (little white boxes) on top of the manifolds.

---

Under floor heating is far neater than radiators, and allows for many different types of floor finish. The system also allows for a high level of flexibility within the house, as each room can be set to a different temperature and heating to differing operating times if required.

---