| 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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Combining direct ground cooling with ground-source heat pumps and district heating: Borehole sizing and land area requirements
- 2022
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Ingår i: Geothermics. - : Elsevier BV. - 0375-6505. ; 106
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Tidskriftsartikel (refereegranskat)abstract
- This article studies the potential combination of direct ground cooling (DGC) with district heating (DH) and ground source heat pumps (GSHP) to compare the required borehole depths and needed drilling areas. It also examines two different borehole sizing approaches to optimize investment costs and drilling areas. The results show that the required borehole depths in most cases are shorter for the DGC and DH combination than for the DGC and GSHP combination. It is also demonstrated that the optimal range of borehole outlet temperatures could be chosen based on the trade-off between borehole installation and terminal units’ costs.
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| 3. |
- Arghand, Taha, 1982, et al.
(författare)
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Combining direct ground cooling with ground-source heat pumps and district heating: Energy and economic analysis
- 2023
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- Direct ground cooling (DGC) is a method used in cold climates to provide cooling to buildings without the use of any mechanical refrigeration. When DGC is utilized for providing cooling, ground-source heat pumps (GSHPs) and district heating (DH) are the two commonly used technologies for providing heating to the buildings. This article investigates the coupling of DGC with GSHPs and DH in terms of purchased energy and lifecycle costs. An office building equipped with active chilled beams for cooling and radiators for heating is used as a reference. Six cases based on different combinations of building envelope characteristics and thus different building heating and cooling loads are considered. The results show that using DGC-DH significantly reduces the amount of purchased electricity. However, the total energy cost is lower when DGC-GSHP is used. In addition, the DGC-GSHP can be more viable when the ground loads are well balanced. Investment costs, including borehole installation and equipment costs, are lower for the DGC-DH in the majority of the investigated cases. The lifecycle cost is lower for the DGC-DH in most of the investigated cases due to lower equipment costs.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Arghand, Taha, 1982
(författare)
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Direct Ground Cooling Systems for Office Buildings
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The solving of crucial global energy challenges hinges on improving energy efficiency in building energy systems. Accomplishing energy-efficiency targets often entails incorporating sustainable energy sources into the energy supply system. Direct ground cooling systems (DGCSs) are among the most sustainable technologies for comfort cooling in office buildings. With this technology, cooling is provided by the circulation of the working fluid through the ground heat exchangers. This technology is mostly used in cold climates where the underground temperature is low, and the building cooling loads are low enough to be offset by the ground cooling. Using only a modest amount of electricity to drive the circulation pumps, this technology is incredibly energy efficient. However, designing DGCSs presents some unique challenges, and only a handful of studies on this subject are available. This work aims to develop knowledge about comfort cooling for office buildings using DGCSs and expand upon design and operation practices for this technology. The findings presented in this work are based on experimental and simulation results. The experimental results build upon existing knowledge for operating cooling systems and substantiate new operation methods for the DGCSs. The experimental results are also used to develop and validate simulations. The simulation results facilitate investigating the short- and long-term thermal and energy performance of the DGCSs for various design circumstances. The borehole system design is usually performed independently from the building energy system design. In view of this work’s findings, considering the whole system (borehole, control system, terminal units) can enhance the design. A sub-system’s input design requirements can be aligned with the corresponding output of other sub-systems in a comprehensive design approach. This work demonstrates and quantifies that terminal units with slow response, such as thermally active building systems (TABS), can smooth out the daily peak heat rejection loads to the ground, resulting in shorter boreholes. Thus, the ground system can be much smaller than required for fast-response terminal units, such as active chilled beams. This work analyses different operation practices for DGCSs. The results suggest that allowing the room temperature to rise somewhat during the “on-peak” cooling loads can reduce the ground heat rejection loads, for which shorter boreholes can be designed. If combined with precooling the space during the “off-peak” cooling loads, a further reduction in the ground loads is yielded. This work also investigates the design and application of the DGCSs in existing office buildings. A systematic approach is provided to evaluate the influence of common renovation parameters on the design and energy performance of a DGCS. The systematic approach includes a step-by-step methodology to explain how sensitive the subsequent system design might be to the variations in the renovation parameters. Furthermore, the results quantify the potential electricity savings by using the DGCS instead of a chiller.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- Arghand, Taha, 1982, et al.
(författare)
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Individually controlled localized chilled beam in conjunction with chilled ceiling: Part 1 – Physical environment
- 2016
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Ingår i: 14th International Conference on Indoor Air Quality and Climate, Indoor Air 2016.
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Konferensbidrag (refereegranskat)abstract
- This study investigates the indoor environment generated by localized chilled beam coupled with chilled ceiling (LCBCC) and compares it with the environment generated by mixing ventilation coupled with chilled ceiling (CCMV). The experiments were performed in a mock-up of single office (4.1 m × 4.0 m × 3.1 m, L× W× H). Thermal manikin was used to simulate room occupant. The LCBCC was placed above the workstation to improve the environment locally. Combinations of indoor temperature of 26 °C and 28 °C and ventilation airflow rate of 10 and 13 l/s were studied. The total heat load in the room was 60 W/m2 (including simulation of solar radiation and miscellaneous heat loads). The results showed that uniform thermal conditions (differences smaller than 1 °K) were generated in the occupied zone with the studied system configurations. The LCBCC diminished the effect of the buoyancy flow from the simulated window and this resulted in more acceptable thermal conditions at the workstation.
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