Electricity + Control August 2017

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TEMPERATURE MEASUREMENT
age of heated and cold water respectively. This
was achieved by two stages of drilling to a depth
of 110 metres at two locations near the hotel.
Summer cooling
In the summer, cool water from the ground, at
7 - 9˚C, is pumped via one set of wells to the
hotel basement, where it is sent through a heat
exchanger removing heat from the hotel internal
air-conditioning circuit. Then it is pumped back
down to a heat reservoir where the heat accumu-
lates and is stored during the warmer months.
In the air-conditioning circuit, water cooled
in the heat exchanger circulates in the building
to cool rooms to the desired temperature. This
cooling system covers 90% of the total cooling
demand with no active refrigeration. Two make-
up combined heat-pumps/chillers guarantee suffi-
cient cooling capacity in peak-load periods.
This part of the process is what results in cool-
ing power 40 times the electricity consumed by
the installation – impressive savings given that it
costs six times more to cool, than to warm water.
Variable Speed Drives (VSDs), on fans, pumps and
compressors in the entire system play a crucial role
in achieving such outstanding energy efficiency.
Winter heating
In winter, water from the underground reservoir,
which has accumulated heat during the summer
period, is pumped through the heat exchanger and
back down to the wells. In the heating circuit, wa-
ter heated via the heat exchanger is sent through
the two heat pumps which further raise the tem-
perature to 55˚C. This heated water is then circu-
lated to warm up hotel rooms and offices.
High efficiency at part load is key
Inside the building, ac drives ensure good control
of the heat pump compressor. The two GEA Gren-
co heat pumps have a combined heat pump perfor-
mance of 2 400 kW and are fitted with -controlled
screw compressors, which enable the system to
adjust the heat capacity continuously from low to
full performance, with an optimum efficiency.
VLT drives ensure good control of pump func-
tion for water circulation to and from the natural
groundwater aquifer. All ground water pumps are
controlled by ac drives in the form of VLT HVAC
Drive FC 102. VSDs are essential for significant
savings and enhanced functionality for the pumps
that propel heat around the hotel’s internal heating
and air conditioning systems.
Conclusion
The ATES system has completely fulfilled expec-
tations as the highly rewarding crown jewel of
the Crowne Plaza Copenhagen Towers’ envi-
ronmentally friendly smart HVAC system, and
the savings have long ago repaid the initial in-
vestment.
<<Author>>
Jesper Thurbo is Global
Director, HVAC at
Danfoss Drives A/S.