| 1. |
- Arghand, Taha, 1982, et al.
(författare)
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A comparative study on borehole heat exchanger size for direct ground coupled cooling systems using active chilled beams and TABS
- 2021
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788. ; 240
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Tidskriftsartikel (refereegranskat)abstract
- Direct ground cooling is a method for cooling buildings whereby free cooling is provided by circulating water through borehole heat exchangers (BHEs). Since no refrigeration cooling is involved, supply water temperature to the building’s cooling system is dependent mainly on BHE sizing. This study investigates the sizing of BHEs for direct ground cooling systems, with a particular focus on the influence of terminal unit types and their operating strategies. Experimental results using a direct ground-coupled active chilled beam (ACB) system are used to develop a simulation model for an office building. The model is also modified for thermally activated building systems (TABS). The simulation results show that using TABS instead of ACBs for a similar BHE reduced the ground peak hourly loads, resulting in a lower borehole outlet temperature. Resizing BHE depth to reach similar maximum borehole outlet temperatures according to the actual heat extraction rate from the cooling systems resulted in a significantly shorter BHE depth with TABS compared to ACBs. However, indoor temperature was generally warmer with TABS, due to their slower heat extraction rate from the room. The findings are practical for analysing the design and operation of BHEs for different types of terminal units.
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| 2. |
- 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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| 3. |
- Arghand, Taha, 1982, et al.
(författare)
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Cooling of office buildings in cold climates using direct ground-coupled active chilled beams
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 164, s. 122-132
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the use of a direct ground cooling system (DGCS) using active chilled beams for the cooling of office buildings in Sweden. The methodology of the study entails laboratory experiments to develop and validate a simulation model of the cooling system. The sensitivity of the input parameters, such as borehole heat exchanger (BHE) length, internal heat gains and room temperature set point, are studied with respect to BHE outlet fluid temperature and room thermal comfort. The results provide a practical insight into designing DGCSs with regard to borehole outlet fluid temperatures. The results also show that the thermal comfort criteria in the room are met by applying the DGCS even under the most critical design conditions of undisturbed ground temperature and internal heat gains. The sensitivity study quantifies the influence of the room temperature setpoint and internal heat gain intensity on the BHE length. The BHE outlet temperature level is more sensitive in shorter BHEs than in the longer ones, and BHE length and room temperature levels are highly correlated. Thus, the sizing of DGCS can benefit from a control system to allow the room temperature to float within a certain range.
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| 4. |
- Arghand, Taha, 1982, et al.
(författare)
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Dynamic Thermal Performance and Controllability of Fan Coil Systems
- 2018
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Ingår i: Cold Climate HVAC 2018: Springer Proceedings in Energy. - Cham : Springer International Publishing. - 2352-2542 .- 2352-2534. - 9783030006617 ; , s. 351-361
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Konferensbidrag (refereegranskat)abstract
- In order to characterize and control a system properly, it is inevitably necessary to understand and define the interactions between various design parameters and the controllability of the system. This study experimentally investigates effects of three design parameters, including supply water temperature, fan speed, and room heat load, on the dynamic response of a fan coil system. The experiments have been performed in a mock-up of an office room equipped with a fan coil unit (FCU). A direct ground cooling system has been used to supply the FCU with high-temperature chilled water ranging between 15 and 23 °C. The dynamic response of the system to step changes in the design parameters has been studied using room operative temperature as an indicator. The results of this study indicate that the system behaves as a first-order system without a time delay. The results also suggest that the time constant and the characteristic of the dynamic response of the fan coil system are not affected by the initial room temperature. Among the design parameters, fan speed is observed to have the most significant effect on the dynamic response of the system. Supply water temperature and room heat load are both found to have insignificant effects on the dynamic response characteristics of the system.
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| 5. |
- Arghand, Taha, 1982, et al.
(författare)
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Energy Renovation Strategies for Office Buildings using Direct Ground Cooling Systems
- 2021
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Ingår i: Science and Technology for the Built Environment. - : Informa UK Limited. - 2374-474X .- 2374-4731. ; 27:7, s. 874-891
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Tidskriftsartikel (refereegranskat)abstract
- Direct ground cooling systems (DGCS) can provide comfort cooling to buildings without the use of any refrigeration-based cooling methods. DGCS is an emerging technology, commonly used for new office buildings in cold climates. This study aims at evaluating the energy-saving possibilities of a DGCS compared to a conventional chiller system for an existing office building. A typical Swedish office building with a chiller-based cooling system and in need of an energy renovation is taken as a reference case. A range of possible renovation measures are applied on the building and the cooling system, and the results are evaluated in terms of borehole design and building energy demand. The results show that applying the DGCS substantially reduces the building’s purchased energy, as chiller electricity demand is eliminated. In addition, implementing the renovation measures to reduce the thermal demand of the building could further reduce purchased energy. The results suggest implementing the DGCS after performing the renovation measures. This may lead to a considerable reduction in the required borehole length and hence, the drilling costs. Results from this study provide useful inputs for designing boreholes in ground-coupled systems for new and existing office buildings.
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| 6. |
- Arghand, Taha, 1982, et al.
(författare)
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Influence of system operation on the design and performance of a direct ground-coupled cooling system
- 2021
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788. ; 234
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Tidskriftsartikel (refereegranskat)abstract
- Sizing of borehole heat exchangers (BHEs) for direct ground cooling systems (DGCSs) is a critical part of the overall system design. This study investigates the thermal performance and sizing of a DGCS with two different operation strategies using experimental and simulation approaches. The traditional on/off operation strategy keeps a constant room temperature. The continuous operation strategy has the potential to reduce the building peak cooling loads by precooling the space and having a variable room temperature measures. The experimental results from the laboratory-scale setup show the differences in the hourly room heat extraction rates and the room temperature pattern for the operation strategies applied. The experimental data is also used to develop a simulation model. The simulation results show that applying the continuous strategy reduces the building peak cooling loads and lowers the heat injection rates to the ground. For new BHEs, applying the continuous strategy can result in shorter BHEs, owing to the significantly lower ground heat injection rates. For existing BHEs, applying the continuous strategy can decrease the borehole outlet fluid temperature and thus, increase the cooling capacity of the building cooling system. The findings of this study have implications for developing the widespread use of DGCSs.
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| 7. |
- 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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| 8. |
- Filipsson, Peter J, 1985, et al.
(författare)
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A thermal model of an active chilled beam
- 2017
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788. ; 149, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Active chilled beams (ACBs) have gained increased recognition as a feasible technology for comfort cooling during the last decades. One of the advantages with such systems is utilization of high temperature cooling. This provides exergetic benefits and also reduces the need for individual room control. However, individual room control normally serves as compensation for the safety margin applied when dimensioning the cooling systems. Therefore, the absence of individual room controls calls for accurate dimensioning tools. This paper presents a model to be used to calculate cooling capacities of ACBs. The model is based on NTU analysis and is a hybrid of first principles and empirical data in order to ensure high accuracy without requiring extensive measurements for model calibration. The model explicitly captures the influence of buoyant forces acting on the air passing the chilled coil in the beam. Output from the model also includes temperature and flow of supply air. The model shows good compliance with measured data in a wide range of operating conditions (average error of 1.7% if six cases is used for model calibration). The model can be appropriately implemented in building performance simulation tools, thus improving the design of ACB systems.
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| 9. |
- Filipsson, Peter J, 1985, et al.
(författare)
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Chilled water temperature control of self-regulating active chilled beams
- 2020
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Ingår i: SINTEF Proceedings. - 2387-4295. - 9788253616797 ; 5, s. 230-237
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Konferensbidrag (refereegranskat)abstract
- The flow rate of chilled water in a self-regulating active chilled beam is constant without respect to the actual cooling load. The cooling capacity is instead determined by the room temperature, which gives rise to the self-regulating effect, and also by the centrally controlled chilled water temperature, which is the focus of this paper . Previous studies have emphasized the benefit of avoiding room-level control equipment, but also highlighted the risk of overcooling with detrimental effects on thermal climate and energy demand. Overcooling may be avoided by supply temperature control, but strategies have not yet been studied in systems operating in cooling mode only. Simulations are carried out with IDA ICE. The results show that overcooling is effectively avoided by proper control of the chilled water temperature. Desired thermal climate is achieved and the energy demand is in the same order of magnitude as in a system with individually and ideally PI-controlled active chilled beams.
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| 10. |
- Filipsson, Peter J, 1985, et al.
(författare)
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Induction ratio of active chilled beams - Measurement methods and influencing parameters
- 2016
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788. ; 129, s. 445-451
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Tidskriftsartikel (refereegranskat)abstract
- In active chilled beams, primary air from the air handling unit induces room air which passes a cooling coil before it mixes with the primary air and discharges into the room. The ratio of induced room air flow to the primary air flow is the induction ratio (IR). Knowledge about the IR is important when modelling cooling capacity as well as temperature and velocity of the air discharged from the beam. Most previous studies of the behavior of IR are focusing on the influence of primary air flow. The purpose of the work presented in this paper is to investigate whether other operating conditions also influence the IR. Three methods of determining the IR are compared in order to strengthen the conclusions. The results indicate that the IR is influenced by the chilled water temperature due to buoyant forces. Novel methods of determining the IR are presented and it is concluded that current methods may lead to overestimation.
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