How tapping into natural resources could take the heat out of energy costs for the Children’s Health Park.
Piotr Rosinski, is the Sustainability, Energy and Technology Advisor on the Health Park’s Project Team. In this feature Piotr drills down to explain how using underground water is just one method to be investigated in the quest for the Health Park to be sustainably energy efficient.
Q: What is an aquifer?
An aquifer is the underground layer of water from which groundwater can be extracted. Aquifers occur in permeable rock (e.g. sandstone) or materials such as gravel, sand or slit.
Due to the existence of permeable rock in the north west and the relatively high levels of rainfall the most productive aquifers can be found here, especially in the Liverpool and Manchester areas.
Q: What is the possibility that the aquifer can be utilised for heating and cooling the Children’s Health Park?
The Trust is investigating the opportunity for using an aquifer for heating and cooling the new hospital.
Q: Was this system of geo thermal energy usage something that the bidders suggested or was it a requirement put forward by the CHP Project Team?
Whilst it is not a specific requirement, the Trust has encouraged both Bidders to consider energy efficiency within the new hospital and the value for money benefits to the Trust and the environment of using innovative ways to heat and cool the Children’s Health Park, of which the aquifer was but one system.
Q: How does the system work and how will the benefits of this system be used in the Children’s Health Park?
In most conventional systems the heat is extracted from the water using a non-reactive stainless steel parallel plate heat exchanger. The parallel plate heat exchange principle is shown in the picture 1 below:
According to Laws of Thermodynamics, the system with the higher temperature will be giving heat to the system with lower temperature until the temperature is equal. Warmer aquifer water will be giving heat to the cold water in a parallel plate heat exchanger. Aquifer water is preheated by the thermal energy of the soil.
The aquifer driven Ground Source Heat Pump (GSHP) does not use the aquifer water itself to heat or cool the building. It only uses the water temperature. Net amount of water extracted for the heating and cooling purposes is zero. The pump will return as much water to the aquifer as it has been taken from it. That is an important point as the water is of drinking quality. Both volumes and water must be preserved.
The heat extracted from the water will be used to drive a vapour cycle compression unit, which may be simply referred to as an industrial sized ‘fridge’.
By using this principle the building can either be cooled or heated, simply by switching between two cycles. The compression unit will either cool or heat the water from the mains which then will be distributed to the heating/cooling panels.
The added advantages are that the vapour compression cycle machines are very reliable and efficient from 1 kW (unit of electrical energy), 5 kW units of heat and/or cooling can be delivered.
Our bidders are expected to deliver a sophisticated solution of detail beyond the scope of this article.
Q: Is it possible to estimate the how much money can be saved using the aquifer system?
This will depend on a number of factors. It is estimated that substantial savings in the region of 30% or even higher could be achieved.
Q: Likewise, what about carbon savings?
We set a target of at least 30% reduction from the current NHS design standard. This needs to be delivered by both bidders.
Q: Do any other hospitals in the UK use an aquifer system for the supply of energy?
Kings Mill Hospital in Mansfield, which is also a PFI funded scheme, uses a similar system to heat and cool all their facilities.
Instead of aquifer they use a lake, but the idea is the same. Kings Mill also operates the largest heating pump in Europe, which is approximately five times bigger than the one that may be installed in the Alder Hey.