Elsevier

Energy and Buildings

Volume 37, Issue 9, September 2005, Pages 920-929
Energy and Buildings

Electrical savings by use of wood pellet stoves and solar heating systems in electrically heated single-family houses

https://doi.org/10.1016/j.enbuild.2004.10.013Get rights and content

Abstract

This study investigates how electrically heated single-family houses can be converted to wood pellets- and solar heating using pellet stoves and solar heating systems. Four different system concepts are presented and system simulations in TRNSYS evaluate the thermal performance and the electrical savings possible for two different electrically heated single-family houses. Simulations show that the electricity savings using a wood pellet stove are greatly affected by the level of comfort, the house plan, the system choice and if the internal doors are open or closed. Installing a stove with a water-jacket connected to a radiator system and a hot water store has the advantage that heat can be transferred to domestic hot water and be distributed to other rooms. Such systems leads to that more electricity can be replaced, especially in houses having a traditional plan. Though it is unnecessary to have too many radiators connected to a stove with a low fraction of energy heating the water jacket. Today's most common control strategy for stoves (the on/off-control) results in unnecessarily high emissions. A more advanced control varying the heating rate from maximum to minimum to keep a constant room temperature reduces the number of starts and stops and thereby the emissions.

Introduction

This study investigates how electrically heated single-family houses can be converted to wood pellets- and solar heating using pellet stoves and solar heating systems. Four different system concepts are presented and system simulations in TRNSYS evaluate the thermal performance and the electrical savings possible.

In Sweden 49 PJ (13.7 TWh) electricity is used for heating in single-family houses and agricultural properties [12]. A little more than 500,000 houses of the 1.5 million Swedish single-family houses are heated with electricity only [6] (agricultural properties and summer houses not included). Together these 500,000 houses use approximately 29 PJ (8 TWh) electricity for heating. This is 6% of the total electricity used in Sweden 2002 [15].

During recent cold winter periods it has been difficult to produce the required peak power in the Swedish electrical grid. The highest peak power measured so far in the grid was 27,000 MW [14]. Assuming that every electrically heated single-family house uses 8 kW electricity for heating at dimensioning outdoor temperature, the total power consumption for 500,000 houses will be 4000 MW (15% of the peak power). Though the benefits from replacing electricity by pellet heating in these houses are besides lower energy costs for the consumer, also a significantly lower peak power in the electrical grid.

Increasing electricity prices and environmental concern makes it desirable to replace electricity for heating purpose with renewable energy sources like biomass and solar.

The possible savings by installing a pellet stove in a well-insulated house that was heated by electric resistance radiators was investigated by [7]. The house has one storey and each room were reached through only one door opening from the hall. The yearly heating demand was 32,040 MJ electricity (domestic hot water not included). The pellet stove that was placed in the living room kept the room temperature at 23 ± 1 °C. The other rooms were kept at a minimum of 20 °C by the electric resistance radiators. Measurements and calculations gave a yearly electricity demand of 6480 MJ/year.

This study investigates further concepts including water-jacketed pellet stoves in two different house types. System simulations are made to make comparisons between different system concepts and different house plans to investigate what parameters having the highest influence on the electrical savings.

Section snippets

House types

This study focuses on converting two different house types from electricity to a system utilizing pellet and solar heating. House type H1 in Fig. 1 has an open plan and type H2 in Fig. 2 is a two-storey house with a more traditional plan. The houses were built during the seventies and have electric resistance heating. The houses have higher heating demands than the house investigated by [7]. The houses represent around 160,000 houses of the total 500,000 electrically heated houses in Sweden [6]

Simulation models

The simulation model for the houses, and the heating systems was built within the TRNSYS 15 environment [4]. The model is described in detail by [10], [11]. The houses were modelled using the TRNSYS Type 56-modell. The different zones are shown in Fig. 1, Fig. 2. Heat transfer between the zones caused by air circulation in openings and doors was calculated according to theory put forward by [2]. The heat transfer in a doorway of 0.68 by 2.0 m depending on the temperature difference is shown in

Simulation results

The energy balance of the houses having only electric resistance radiators and an electric heated hot water store is shown in Table 4. Fig. 12 shows the simulated results for systems S1 to S3 for the two house types. The simulation results are presented as the fraction of electricity, pellet and solar energy being supplied to the house. The pellets energy is the energy content of the pellet being consumed by the stove and the electricity consumed is for auxiliary heaters, radiators, pumps, and

Discussion

The systems that are simulated in this study are not perfectly optimised, but the further optimisations possible are judged to be small compared with the influence that the different users can have on the performance.

The uncertainties in the simulation model are mainly the approximation of the whole zone having the same air temperature. Uneven air temperatures in real houses can mean that radiators do not turn off due to cold air coming from ventilation inlets or windows. Due to this factor,

Conclusions

The electricity savings using a pellet stove are greatly affected by the level of comfort, the house plan, the system choice and whether the internal doors are open or closed. For house type H1 with an open plan, around 80% of the electricity for heating can be replaced by installing a pellet stove without a water jacket. The internal doors should be open and a temperature difference of about 3 °C between bedrooms and the living room has to be accepted. To achieve the same electrical savings

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