Health
Kendray MHU – Ground Source Heat Pumps
Completed through the Procure 21 Framework, Kier Health, in partnership
with Barnsley Primary Care Trust, has completed a new purpose built acute
mental health unit to provide high levels of adult care in a pleasant and safe environment. The
building provides a modern state of the art facility in which to carry out psychiatric intensive
care and incorporates private and group therapy areas, activity spaces as well as having
separate male and female wards.
Central to the design solution was the need to provide a natural environment incorporating
sustainable features and creating therapeutic themed gardens that also serve to enhance local
biodiversity. Key building materials such as timber cladding and recycled aluminium alloy roof
cladding have also been used. The main circulation areas promote social interaction and
utilises natural daylighting from high level windows and rooflights.
The development of the design and sustainable technology solutions has recognised the NHS
strategy to reduce carbon emissions. The potential for low energy design and reducing carbon
dioxide output by the new unit was considered from the outset with framework consultants
Race Cottam Associates and WSP carrying out a number of early feasibility studies.
With the anticipated rise in gas and electricity tariffs over the coming years the need for
sustainable design solutions is becoming increasingly more important to reduce not only global
warming potential but also to improve upon running and operating costs.
Passive means of reducing solar gains were explored and by carrying out modelling of the
building using specialist software the incidence of high internal temperatures were reduced.
The nature of the building led to considering the benefits of providing lower surface
temperatures to ensure patient safety combined with lower running costs and emissions.
Underfloor heating was selected as the preferred solution to achieve this.
In order to facilitate a sustainable design solution ground source heating and cooling was
proposed on the basis that this also performs very well with low grade heating requirements
such as that used in underfloor heating.
The earth absorbs nearly half of sun’s energy amounting to over 500 times more energy than is
currently needed by the population each year. Geothermal heating is a renewable heating
resource using the earth’s energy storage capability. At a local level the suitability and
affordability for utilising this stored energy depends largely upon the site geology and assessing
other constraints.
In association with
Ground source heating utilises the relatively constant nature of
the ground temperature and converts this through a heat pump
to useable heat energy. The heat transfer within the ground is
carried out using a ‘closed loop’ system comprising ‘U’ tube
pipework placed within deep boreholes set out in a grid array.
The depth and spacing of the boreholes is determined following
a ground thermal response test initiated from a trial borehole.
The pipework is in turn grouted within the borehole to ensure
good thermal conductivity is maintained.
The performance and selection of ground source heating relies
on achieving an appropriate Coefficient of Performance (CoP)
where the amount of heat energy obtained is measured against
the electrical input energy. Typical CoPs’s are presently around
3.5 – 4.0 representing upto 4 times the amount of extracted heat
energy available as compared to the electrical input energy used
in operating the system. A higher CoP is achieved when the unit
is used in reverse cycle for cooling.
The heat pump capacity for the new Mental Health Unit is sized
at 80 kW and in conjunction with a storage buffer will serve
approximately 70% of the underfloor heating load. 12 No.
boreholes each 100m deep have been provided to achieve this
duty. The estimated reduction in carbon emissions equates to in
excess of 3 tonnes per annum or around 156 tonnes for the
design life of the installation. The system is supplemented by
high efficiency gas fired condensing boilers during times of peak
demand.
By operating the heat pump cycle in reverse it has also been possible to activate beneficial
cooling during warmer periods which will allow heat from the underfloor circuits to pass
through the heat exchanger from which the heat is then rejected back into the boreholes. This
will assist in providing lower internal space temperatures during peak summer times to
improve comfort conditions as well as helping to regenerate the borehole field.
Whilst payback periods are difficult to predict against the current trend of variable and rising
tariff charges of traditional energy sources there is a sustained benefit in achieving reduced
emissions of carbon dioxide, increased operational efficiencies and in supporting the drive of
the NHS to make continuous improvement towards reducing its energy consumption across the
whole NHS Estate.