Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
This thesis is to study the feasibility of using river water from Gavleån in the cooling system of University of Gävle. The project is proposed by the campus service manager Akademiska Hus AB which intended to replace the current cooling production system with the water cooling system to reduce the electricity cost in cooling production. The river by direct distance is 600 meters from the university, the river water is to be extracted from the river via a pump house, flow through pipeline buried underground and delivered to the equipment house of Akademiska Hus.
Most water source cooling prefer water body with decent depth which contain low temperature water to use as free cooling source, but the issue that limits the practice is, the decent depth is not a very common feature of most water body near or within urban area. Like Gavleån which has an average depth of not over five meters while the sufficient depth is over 50 meters for the least or 70 meters to 100 meters often. So study the potential of using rather high temperature water from shallow water body can be of high interest for most cooling consumers.
The thesis progressed through the work in five parts. To introduce cooling in general starting with literature review, the concept, the mechanism, the device for end use and production, the demand of cooling and the reason behind it. Followed by case studies of water source cooling projects worldwide, which is mostly deep water source cooling, and another case of the local hospital cooling system that extract water from Gavleån, demonstrate the use of shallow water body in assisting cooling production, it gives some insights how the potential if similar system is to be implemented in the campus, which is mounted on the same river. Several tours to the hospital were taken to acquire data and understanding of the system.
Then the water temperature measurement from Gavleån in 2014 summer is presented. The measurement was carried out at a small dock by the river side during July to September of 2014. The measurements show the temperature of river water has been increasing which limits free cooling throughout the year, additional refrigerator is required to produce chilled water. The river water, in the hot seasons is used as cooler for the refrigerator and in cold season can be used for free cooling directly. Simulation of IDA-ICE gives the cooling demand of modelled building blocks, the output of cooling production season (consistent with the hot seasons) matches the cooling consumption data from Akademiska Hus by an error of 1% (414743 kWh of simulated result to 415270 kWh in documentation of Akademiska Hus).
To meet the demand of cooling and select more cost-effective refrigerator type, consumption and COP (COP: Coefficient of Performance) are calculated for compressor chiller and absorption chiller with basic cooling cycle for both. The results shown compressor chiller has much better performance but also higher consumption in electricity, while absorption chiller has rather low COP value in comparison but the need of energy input is much less given by its major consumption of energy is heat from hot water, already a purchased item by the university from district heating network. Cost-effectiveness wise speaking absorption chiller is a more optional choice. Reasonable values of assumption are largely employed in the calculation to select the better candidate and bring certain errors, which is then exam in sensitivity analysis to weigh the alternative parameter and the outcome from it.
The last part is to estimate the cost of chillers and pipeline, for the concern of minimizing errors due to uncertainty the operation cost, labor cost and future energy price are not included. As the calculation turns out the payback year of the new system can range from 7 to 12 years by different refrigerator setup and pipeline routine design, which is considered within the life time of the chiller and pipeline, also lower than the current cooling cost of the university and therefore concluded as promising investment.
Discussion and conclusion exam and finalize the whole thesis work. For the uncertainties of the calculation, the lack of information and data, which are improvements, can be done in future work. Also the improvements in other perspectives noted in terms of better load management for the cooling production units so the cost of equipment can be reduced, changes in building attachment and cooling device to reduce the demand of cooling, etc. But mostly draw the conclusion that with proper system configuration shallow water body can be helpful in reducing cooling consumption, and be a promising option for cities that have access to such water body.
2015. , 94 p.
Water Source Cooling, River Water, Gavleån, Refrigerator, Simulation, Building cooling consumption