| 1. |
- Arghand, Taha, 1982, et al.
(författare)
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Control methods for a direct-ground cooling system: An experimental study on office cooling with ground-coupled ceiling cooling panels
- 2019
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788. ; 197, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- This article experimentally investigates the performance of two control methods (the supply water temperature method and the water flow control method)for a direct-ground cooling system. The control methods were implemented through three types of indoor feedback controllers: 1)an on/off controller, 2)an on/off controller with a deadband and 3)P controller. The performances of the control methods were evaluated regarding room temperature stability and pump energy use. Ceiling cooling panels were employed to keep the test room air temperature at 25.0 °C under periodic heat gain conditions. The cooling system used a ground heat exchanger with a U-pipe in an 80-meter-deep borehole as a cooling source. The findings show that room air temperature was maintained close to the set-point with both control methods, but it was more stable with the temperature control method. In addition, condensation risk was easily preventable with the temperature control method. A parametric study showed that pump energy use when using two-position controllers could be as low as when using modulating controllers if the on-state flow rate of the circulating pump is selected in relation to the ground temperature and heat transfer characteristics of the heat exchanger.
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| 2. |
- Arghand, Taha, 1982
(författare)
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Direct-Ground Cooling Systems for Office Buildings: Design and Control Considerations
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Direct-ground cooling systems are defined as systems in which the ground is used as the only source for cooling mainly in commercial buildings. These systems benefit from exchanging heat with the ground, of which its temperature is basically constant below a certain depth year around. Since electricity demand of these systems is only about driving the circulation pumps, the direct-ground cooling systems are among the most environmentally sustainable and energy efficient systems available for cooling buildings. This thesis is undertaken with a two-fold aim: presenting the design parameters of the ground-coupled systems, and evaluating the methods for controlling the cooling capacity of the direct-ground cooling systems. A comprehensive literature review has been performed on three main design parameters for the ground cooling systems, including ground thermal properties, borehole thermal resistance and building thermal load. All these parameters have been investigated regarding their influence on the energy demand of the system. The literature survey has been further extended to the terminal units operating with high-temperature chilled water, as they are suitable indoor heat terminal units for the direct-ground cooling application. The most common high temperature cooling terminal units have been studied regarding their working temperature levels and cooling capacities. Control methods for direct-ground cooling systems is the second major aspect studied in the present work. Two control methods, supply temperature control method and flow rate control method, have been applied to a ground-coupled ceiling cooling panel system and a fan-coil unit in laboratory settings. The experiments have been conducted in an office-scaled test room under different thermal indoor climates and heat gains. The results have shown that the design of the control system shall be done in relation to the flow rate limits in the building and ground loops, and the temperature levels of the ground. A high flow rate in the ground loop or in the building loop will not enhance the cooling capacity of the terminal units, but only caused increase in the energy use of the circulation pump. On the other hand, too low flow rate in the building loop increases the condensation risk on the pipes. This is because the supply water temperature in the building loop became closer to the ground temperature which is below the dew point of the space.
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| 3. |
- Arghand, Taha, 1982, et al.
(författare)
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Some aspects of controlling radiant and convective cooling systems
- 2019
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Ingår i: E3S Web of Conferences. - : EDP Sciences. - 2555-0403 .- 2267-1242. ; 111
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Konferensbidrag (refereegranskat)abstract
- This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 Designing appropriate control systems for radiant heating and cooling terminals entails an understanding of their dynamic behaviour. This study experimentally investigates the dynamic response of a room with convective and radiant cooling systems. The experiments were performed in a 12.6 m2 large test room outfitted as a single-office room. The main cooling system was radiant ceiling panels which covered 70% of the ceiling area. The thermal performance of the radiant system was compared to that of a fan-coil unit (FCU). The results from the step response test showed that the time constant of the room for the radiant system was shorter than for the convective one, indicating faster changes in room temperature by the radiant system. Furthermore, controlling the FCU with similar control system tuned for ceiling panels increased the hysteresis gap in the room air temperature from 0.4 K to 0.8 K. This indicates that control systems for low-mass radiant systems and convective systems might be applied to each other, but on-site tuning is required to omit the offset (persistent error). In this study, controlling room temperature with ceiling panels did not benefit from using an operative temperature sensor to provide feedback signal to the control system. However, the pump energy use was moderately decreased by 14%.
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