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Energy and Environmental Considerations
Published in John Knight, Peter Jones, Newnes Building Services Pocket Book, 2012
Free cooling is a term used for the reduction or elimination of mechanical refrigeration load by using outside air instead of recirculated air, or by the operation of the refrigeration plant as a thermosiphon, the compressor then being off. When used in an all-air system of air conditioning, such as most VAV plants, it means that if the outside air enthalpy is lower than the enthalpy of the return air there is a reduction of refrigeration load by using all outside air. When the outside air temperature is at or below that required off the cooling coil, the refrigeration load is zero and the refrigeration plant can be shut down. This temperature is typically about 10°C and by using the BSRIA data [2] on the occurrence of wet and dry bulb temperatures it can be seen that the dry-bulb temperature is at or below 10°C for about 59 per cent of the year.
Application of Fuzzy Logic for Control of Heating, Chilling, and Air Conditioning Systems
Published in Ali Zilouchian, Mo Jamshidi, Intelligent Control Systems Using Soft Computing Methodologies, 2001
An important aspect for the formulation of the rules for this controller is the cooling potential of the system, which is represented by the input variable 3 , Δ Tout. The higher the value of this variable is, the fewer free cooling system components are necessary in order to supply the demanded cooling power for the building. Producing the cooling power by free cooling system reduces the cost of the cooling energy and the operation time of the cooling machines. This controller consists of 29 rules.
Software/Application Programs
Published in Richard A. Panke, Energy Management Systems and Direct Digital Control, 2020
During the summer cooling season it is not unusual for the outdoor air temperature to drop considerably at night. Frequently, during the early morning hours prior to building occupancy time, the outdoor air temperature is below building space temperatures. This cool outdoor air can be utilized to cool the building, thereby eliminating the need for mechanical cooling during early morning occupancy hours. This free cooling will generate energy savings and also save wear on the mechanical cooling equipment.
Modelling of rooms with active chilled beams
Published in Journal of Building Performance Simulation, 2020
Peter Filipsson, Anders Trüschel, Jonas Gräslund, Jan-Olof Dalenbäck
A key opportunity with ACBs is utilization of high-temperature cooling. In this paper, high-temperature cooling refers to a chilled water supply temperature of ≥20°C. This provides major benefits such as increased use of free cooling, efficient operation of chillers, reduced latent load, reduced risk of condensation, reduced thermal losses in the chilled water distribution system and, due to self-regulation, less need for individual room control (Maccarini et al. 2017). Higher chilled water temperature and supply air temperature are also beneficial for the IR (Filipsson et al. 2016) and for the supply air plane jet attachment (Wu et al. 2018) respectively. Filipsson et al. (2020) present a high-temperature ACB system in Stockholm, Sweden, with neither chillers nor room thermostats. The water is chilled in boreholes and by preheating incoming outdoor air (when needed). Due to the self-regulating characteristic of high-temperature cooling, there is no individual room control of the chilled water flow rate.
Assessments of demand response potential in small commercial buildings across the United States
Published in Science and Technology for the Built Environment, 2019
The thermostat demand-limiting control implements a strategy that precools the building in early morning to store “cooling” energy in the building thermal mass and then adjusts the building temperature upward during on-peak periods. This strategy can shift cooling loads from high electricity price periods to low price periods and reduce peak electrical demand. In addition, the precooling strategy can take advantage of the lower ambient temperature in early morning. The advantages include “free” cooling opportunities through use of cool outdoor air to reduce mechanical cooling and also higher mechanical system cooling efficiency due to greater operation at lower ambient temperatures. The thermostat demand-limiting control solves a simplified optimization problem that handles both energy and demand charges and that is based on experiences and methods from previous studies. The overall approach is somewhat similar to that proposed by Henze et al. (2008) where sequential daily optimizations are performed that are constrained by a target demand threshold but also employs a demand-limiting algorithm based on Lee and Braun (2008d). Rather than determining a demand constraint with a month-long optimization, a demand threshold is set to an initial value at the start of each month and then updated each day. Although this is not the optimal solution, it is an approach that could be readily implemented in practice using a model predictive control solution with a relatively short prediction horizon. In addition, rather than simply a peak power demand constraint, the constraint is expressed as a demand cost constraint in order to enable more complex rate structures with multiple rate periods and demand charges.