90% energy savings thanks to smart HVAC alone?
Yes. The ground water heating and cooling system installed here is known as Aquifer Thermal Energy Storage (ATES). ATES is an innovative open-loop geothermal technology, in use at over 1000 sites mainly in Scandinavia and the Netherlands as an energy-conserving measure for large buildings.
It’s gaining popularity with good reason. For a start, it can reduce the total energy consumption for cooling and heating of a building by approximately 70%; and more than 90% for cooling alone, compared to conventional technologies.
The ATES system delivers a coefficient of performance (COP) of up to 40, which means that the cooling power is up to 40 times the electricity consumed by the installation. Normally the COP for a building of this size would be only 4 or 5.
The Danish expert in ATES is Stig Niemi Sørensen, Ph.D., who explains it like this: “Natural groundwater reservoirs are well-suited to the storage of thermal energy over long periods. The use of ATES technology is well-proven to enable a significant reduction in energy consumption and therefore in CO2 emissions arising from fossil-fuel-based energy production. An ATES plant is easy to establish and has only limited thermal effect upon the natural groundwater reservoir. It can be established in a manner that ensures no conflict with groundwater extraction for drinking water supply.”
Venture into new territories pays off
Allan Agerholm (Chief Hospitality Officer, BC Hospitality Group A/S) was on the Crowne Plaza team who originally established the ATES system, and sums up the results like this:
“When you venture into new territories, as we did, putting in the first groundwater based heating and cooling system in Denmark, you’re always a little bit worried; will your partners deliver? And I have to say that working with Danfoss on this project has been a tremendous success. We’ve had very few challenges. In fact, the system has delivered precisely what it was calculated in theory to do; that is to deliver in the region of 90% energy savings during the summer months, and in the region of 60% during the winter, which is really outstanding.”
So how does it work?
The Crowne Plaza ATES used a suitable natural groundwater reservoir, known as an aquifer, into which two thermal wells were installed, for storage of heated and cold water respectively. This was achieved by two stages of drilling to a depth of 110 meters 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’s pumped back down to a heat reservoir where the heat accumulates 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 sufficient cooling capacity in peak-load periods.
This part of the process is what results in cooling power 40 times the electricity consumed by the installation – impressive savings given that it costs 6 times more to cool, than to warm water. Variable speed drives 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, water heated via the heat exchanger is sent through the two heat pumps which further raise the temperature to 55˚C. This heated water is then circulated 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 Grenco heat pumps have a combined heat pump performance 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 optimum efficiency.
VLT® drives also ensure good control of pump function for water circulation to and from the natural groundwater aquifer. All groundwater pumps are controlled by AC drives in the form of VLT® HVAC Drive FC 102. Variable speed drives are also essential for significant savings and enhanced functionality for the pumps that propel heat around the hotel’s internal heating and air conditioning systems.
The ATES system has completely fulfilled expectations as the highly rewarding crown jewel of the Crowne Plaza Copenhagen Towers’ environmentally friendly smart HVAC system, and the savings have long ago repaid the initial investment.
Author: Jesper Therbo, Global Director – HVAC, Danfoss Drives