A Ground Source Energy Plant for the New Assembly for Wales

The new National Assembly for Wales in Cardiff Bay has been completed in September 2005. This event was not only a political achievement but also a milestone in environmentally friendly building. Architect Lord Richard Rogers’ key in the design formula were sustainability and innovation. The designers accomplished this by using local materials and bringing waste to a minimum. Another feature of this environmentally conscious building style is the natural ventilation and temperature control. The marked funnel on the roof is not only a defining feature of the architecture but also a functional design, as it enhances natural ventilation, rejecting warm air and allowing cooler air to be drawn in. As a source of heat and cool a system of ground source heat pumps is installed, that allow very efficient heating and cooling, making use of the earth beneath the building. For the New Assembly for Wales building Groenholland developed a new approach of applying ground source heat pump technology. Often, when both heating and cooling are required, the heat pump is reversed, the function of the condenser and evaporator are changed. This means that the building is the “warm side" in winter and the “cold side" in summer. It also means that only heating or cooling is possible at any given time. While very efficient and practical in many situations, it is not possible to cool and heat concurrently. We therefore developed a system that primarily transfers heat from the air conditioning system to the heating system. The ground loops are coupled to the side that requires the lowest load at a given time. For instance, in summer the building will be dominated by cooling and the heat pumps will generate excess heat, the “warm”side of the heat pumps will then be connected to the building and the ground loops. The control software developed by us allows the system to operate completely autonomously, even a connection to the building control system is not needed. An integrated design approach was followed, where a careful analysis of the interactions between the different components was made. The goal was to design a plant that can provide the full capacity needed, but that is optimized to provide the average capacity at the highest efficiency possible. Several novel approaches were implemented, both on the hardware level and in the control software. The final plant is of high efficiency and of very compact design, allowing significant space-savings as well.