Latent värmelagring i vattenburet uppvärmningssystem med elpanna för byggnadsapplikationer
Latent heat storage is a way to store thermal energy when a phase change material undergoes a phase change. The advantage of latent heat storage is the capability to store more energy per mass unit than other heat storage methods. The most commonly used phase change in latent heat storage is the transition between solid and liquid. Phase change materials can be divided into organics, inorganics and eutectics.In the Nordic electricity market the price of electricity is set every hour by Nordpool spot, which leads to price fluctuations because of changes in demand. The main goal of this report is to create a latent heat storage system in a single-family home and investigate the possibility to save money by charging the latent heat storage system when the price of electricity is low, and discharge when the price is high.The thermodynamic model consisted of a ?tube-in-tube? heat exchanger with phase change material in the outer tube and water as the heat transfer fluid in the inner tube. The model is based on the assumption that the phase change is an isothermal process. By the use of assumptions and mathematical correlations, the heat transfer between the phase change material and heat transfer fluid was calculated. The latent heat storage system was a heat complement to a waterborne heating system, and supposed to be connected to an electric water heater. The latent heat storage uses water as heat transfer fluid in a temperature range of 79-87 °C.The profitability of the latent heat storage system was investigated in an economic model through two investment calculation methods, net present value and payback. The cost savings per year was estimated by comparing the cost of electricity with and without a latent heat storage system during the period 2011-10-01 to 2012-03-31. A sensitivity analysis was made in both the thermodynamic and economic model.The results of the thermodynamic model was that the latent heat storage system had a storage capacity of 14,8 kWh, discharged in 3 hours and was charged in 3,1 hours. The heat transfer was calculated to 4,8 kW during discharge and 4,7 kW during charge. The economic model indicated that the investment in a latent heat storage system was not profitable. The payback time was calculated to 28 years and the net present value was calculated to -28 691 SEK. The cost savings per year was 1425 SEK/year and the initial investment was estimated to 39 965 SEK.The thermodynamic model is to be considered crude because of made simplifications and assumptions. These assumptions lead to a better performance than what should be expected in reality. This considered, lead to the fact that there is no economic profit in the present condition of the latent heat storage system. Usage of latent heat storage systems on a large scale may however have environmental profits. By increasing the storage capacity and decreasing the initial investment cost the latent heat storage system would be more economically profitable. If the number of days with great variations in the price of electricity would increase it would also lead to a more economically profitable latent heat storage system.