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| 2. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Factorial design for energy System Models
- 1994
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 19:8, s. 905-910
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Tidskriftsartikel (refereegranskat)abstract
- Mathematical models are extensively used in energy analysis and have increased in scope as better and faster computers have become available. With complicated systems, it is difficult to predict accurate results if doubtful input data are changed. Traditionally, sensitivity analysis with a change of one or more of the parameters is used. If the influence of a change is very small, the first result is believed to be accurate. Problems may arise when sensitivity analysis is applied to a vast amount of data. The aim of this paper is to examine whether the calculation effort can be decreased by using factorial design. Our model, called Opera (Optimal Energy Retrofit Advisory), is used to find the optimal retrofit strategy for a multi-family building. The optimal solution is characterised by the lowest possible life-cycle cost. Three parameters have been studied here: length of the optimisation period, real interest rate and existing U-value for an attic floor. The first two parameters are found to influence the life-cycle cost significantly, while the last is of minor importance for this cost. We also show that factorial analysis must be used with great care because the method does not reflect the complete situation.
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| 3. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Heat Accumulators in CHP Networks
- 1992
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Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 33:12, s. 1051-1061
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Tidskriftsartikel (refereegranskat)abstract
- In a Combined Heat and Power (CHP) network, it is sometimes optimal to install a device for storing heat from one period of time to another. Several possibilities exist. If the electricity demand is high, while at the same time the district heating load is too small to take care of the heat from the CHP plant, it could be optimal to store heat from peak periods and discharge the storage under off-peak. It might also be optimal to store heat during off-peak and use it under the district heating peak load. The storage is then used for decreasing either the district heating demand or for decreasing the electricity load used for space heating. The paper shows how a mixed integer program is developed for use in the optimization process. As a case study, the CHP system of Malmö, Sweden, is used. Further, a sensitivity analysis is elaborated in order to show how the optimal solution will vary due to changes in certain input data.
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| 4. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Is space heating in offices really necessary?
- 1991
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 38:4, s. 283-291
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Tidskriftsartikel (refereegranskat)abstract
- New office buildings in Sweden are thoroughly insulated due to the Swedish building code. This code, however, does not consider the type of activity occurring in the building. This means that the heating equipment is designed as if no activity at all is going on. In modern offices there is a lot of equipment installed which uses electricity. This electricity is converted into heat which can be utilized for heating the premises, mostly in a direct way but also by the use of exhaust-air heat-pumps or heat exchangers. This paper deals with a modern office building plus office hotel complex located in Linköping, Sweden, about 200 km south of Stockholm. The tenants deal with the design of hard- and software for computers. The lighting and computers in the building use electricity which converts into heat. In this paper, it is shown that this electricity is all that is needed during normal conditions, i.e. when people work in the building. The building is also equipped with a district-heating system, which is designed as if no activity goes on in the building, so subsequently the heating equipment is larger than it need be. In this special case, it might have been better to install an electric heating device for hot-water heating and very cold winter conditions, instead of using district heating. This is so even if district heat is about half the unit price compared with that due to the dissipation of electricity. At present, when district heating is used, no measures for saving heat can be profitable due to the low district-heating price. The fact is that the tenants complain of too much heat instead of too little: the prevailing indoor temperature was about 24° C in January 1990 even though 20° C would have been sufficient. There is subsequently a need for a properly working regulation system. The one currently in use is designed to a modern standard, but is not able to maintain temperatures at a modest level.
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| 5. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Linear Programming Optimization in CHP Networks
- 1991
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Ingår i: Applied Thermal Engineering. - 1359-4311 .- 1873-5606. ; 11:4, s. 231-238
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows how to simulate a CHP network (CHP = Combined Heat and Power) using the method of linear programming. This method makes it possible to optimize the mathematical model and subsequently find the very best combination of electricity production, electricity purchase and heat production in a district heating system. The optimal solution in the model is characterized by the lowest possible operating cost for year. The paper shows the design of the mathermatical model and furthermore a case study is presented using the district heating net in Malmö, Sweden, as an example.
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| 6. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Natural gas in Optimized Bivalent Heating Sytems
- 1990
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Ingår i: Energy. - 0360-5442 .- 1873-6785. ; 15:11, s. 993-999
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Tidskriftsartikel (refereegranskat)abstract
- In accordance with a public referendum held in 1980, Sweden will phase out nuclear power completely by 2010. One way to compensate for an immediate, appreciable scarcity of electric power is to construct new fossil-fuel power stations. Another is to reduce the burden on electric power by converting some end-user facilities to operate on natural gas (NG) imported from Denmark through a new pipeline to southern Sweden. We show how an optimal solution can be found for NG operation of a system incorporating an NG boiler and an electric heat pump. Electricity is priced by a time-of-use tariff (TOU) requiring a discrete optimization method. The optimal solution is characterized by the lowest life cycle cost (LCC) for the building as an energy system.
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| 7. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Production or Conservation in CHP Networks
- 1990
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Ingår i: Heat Recovery Systems and CHP. - 0890-4332. ; 10:2, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- In Sweden, Combined generation of Heat and Power (CHP) is in common practice. Different fuels are burnt in a boiler and the steam is used for generating electricity. The heat that has to be transferred from the condenser in the plant is used in the district heating grid. This grid is thus used as a cooling facility necessary for electricity production. However, energy conservation the Swedish building stock is also encouraged, and if this is utilized in district heated buildings it results in fewer possibilities for electricity production. This might be a major drawback when nuclear power is abolished, as is the result from a consensus some years ago. This paper deals with the question of whether it is better to conserve both heat and electricity, to save only one of the energy forms or if it is cheaper to produce more energy, instead of saving. A case study is presented dealing with Malmö, in the South of Sweden, and it is shown that energy conservation in district heated buildings cannot yield profitability: neither can conservation in the electricity grid, even if it gets closer to profitable savings. It is assumed that the total cost of heating, insulation and electricity is paid by the society and the minimum point for this cost will characterize the best solution.
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| 8. |
- Gustafsson, Stig-Inge, et al.
(författare)
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Window Retrofits : Interaction and Life-Cycle Costing
- 1991
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Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 39:1, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the interaction between different types of building energy retrofits. The means for finding this interaction has been via the OPERA model, which is used for energy retrofit optimization. The solution is an optimum when the total life-cycle cost, LCC, for the building, i.e. the sum of the building, maintenance and operating costs, is minimized. The model finds the candidates for the optimal strategy by calculating the total LCC for one retrofit after another, i.e., an incremental method is used. All the measures are implemented with respect to the building and the resulting LCC is calculated. Usually, the LCC for this combination is higher than the incremental LCC, i.e. the incremental way of calculation overestimates the savings. However, when window retrofits are considered, the opposite might happen due to the use of shading factors. These factors indicate the decrease in solar radiation through a window when an ordinary one is replaced by a window with enhanced thermal performance. The paper also shows that the interaction between the different measures usually can be neglected, as long as optimal retrofits are introduced.
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