The chiller that can also heat
The development of a new range of water-cooled chillers by Carrier offers the possibility of integrating a building’s need for sources of heat and cooling into one item of plant.
Responding to climate change demands a 2-pronged approach. One is to mitigate its effects by reducing carbon-dioxide emissions, including the 40% that are associated with buildings. The other is to adapt to its effects, one effect of which is an increased demand for air conditioning.
Meeting such an growing need for air conditioning while reducing energy consumption and associated carbon-dioxide emissions drives the development programmes of major companies.
Carrier, for example, has been steadily improving the efficiency of its chillers in the long term.
Even before legislative measures to reduce the carbon footprint of buildings such as the current Building Regulations requiring new air-conditioned buildings to use about 25% less energy than a building of the same function designed to 2002 Building Regulations, Carrier was already making huge strides in improving the performance of chillers.
Just how much the energy efficiency of chiller has improved is summarised by Didier Da Costa, Carrier’s operations director for building systems and services for Europe, the Middle East and Africa (EMEA). He says that efficiency has doubled since 1995.
As an example, a reciprocating chiller dating from 1995 and using R407C would have had an EER of 3.
Its latest liquid-chiller range, the water-cooled Aquaforce 30XW achieves a full-load EER of up to 6.2 and an ESEER (Eurovent Seasonal Energy Efficiency Ratio) as high as 8.1. Those figures are significantly better than Eurovent’s energy-efficiency classification for water-cooled liquid chillers, which requires an EER at full load of 5.1. Additionally, these chillers are up to 20% more efficient than their predecessors.
The introduction of Aquaforce water-cooled chillers follows the launch of the Aquaforce air-cooled range in 2006. Kelly Romano, president of Carrier building systems and services, says, ‘The launch of Aquaforce chiller reinforces Carrier’s position as a world leader in environmentally responsible commercial heating, ventilation and air-conditioning solutions.’
The introduction of these chillers comes at a time when the demand for water-cooled chillers in Europe is growing. In 1999, explains Badir Bensaidi, marketing product manger for building systems and services for Carrier’s EMEA region, the split between water-cooled and air-cooled chillers was 12/88%. The proportion of water-cooled has now doubled to 24%.
Although using cooling towers to reject heat from a chiller is inherently more efficient than air-cooled condensers, water-cooled chillers offer more engineering opportunities to boost efficiency and to integrate with renewable-energy sources — as indicated later. In particular, these latest Aquaforce chillers can deliver water at up to 63°C for space heating and generating domestic hot water. Their COP for such applications can be above 6.5
There are 27 models of these chillers with cooling capacities from 400 to 1800 kW. They use R134a with a new generation of twin screw compressor with rotors optimised for water-cooled chiller operation and variable slide valve capacity control down to 15% of maximum capacity.
The heat exchanger is of the flooded design to maximise energy transfer between the chilled fluid and refrigerant. A further boost to efficiency is imparted by micro-grooves on the internal and external surfaces of the water tubes to increase surface area and enhance heat transfer.
An economiser section with an electronic expansion device improves cooling capacity and operating efficiency.
The smaller units are designed with the key components in a vertical configuration, so that even units with a cooling capacity of greater than 1 MW are only a metre wide and can fit through a standard plant-room door — a valuable feature for refurbishment projects.
Developing such a new range of chillers takes a couple of years, and it was in September 2007 that the first units were submitted for laboratory testing.
Products have also been tested on customer sites, one being the aquarium in Lyon in France, close to Carrier’s factory and research and development facility at Montluel.
The installation at the Grand Aquarium de Lyon gives an insight into the engineering potential of these water-cooled chillers. The aquarium opened in 2002 and has 44 different tanks accommodating more than 270 species from piranhas to the white tip reef shark, which can grow up to 2.3 m long.
The largest tank is 8 m deep and contains 500 000 m3 of water that must be maintained at 20°C with a maximum variation of ±1 K.
Water-temperature requirements in other tanks range from 12°C for trout to 27°C for tropical fish.
A single Aquaforce water-cooled chiller is at the heart of a system that simultaneously provides both heated and chilled water to serve the requirements of the various tanks and control of room air temperature.
The installation comprises 14 plate heat exchangers, seven for cooling and seven for heating, and additional electric heaters for the tanks that require heating to 27°C. There are also nine air-handling units to maintain air temperatures from 20 to 23°C to create different ambiances. Chilled water is delivered at 5°C to provide cooling for the room air-conditioning system and the cooling needs of the tanks. Hot water is delivered at 45°C for room air heating and for tanks that require heating.
To a large extent, heating and cooling requirements balance, and any imbalance is made up by rejecting heat into a 15 m-deep borehole or drawing heat from two boreholes — also 15 m deep. The aquarium is at the confluence of two major rivers, the Rhone and the Saone, so the ground is saturated with water with an average temperature of 15°C over a year and providing a source of renewable energy.
While the scope for matching heating and cooling requirements offered by an aquarium will not be reflected by comfort building-services applications, the capabilities of such water cooled chillers offer an intriguing insight into the future.