Climate effects of heating buildings

Heating buildings in Finland

The two most widespread methods to heat buildings are district heating and electricity (Figure 1). District heating is the most common means of producing heat energy in towns. More than 90% of residential blocks of flats are in the district heating system, while the number of detached and semi-detached houses is considerably smaller.

District heat is produced in combined heat and power plants (CHP) or central boiler plants. CHPs are the most energy-efficiency option. Surplus heat from the industry and heat from landfill gas can also be fed to a district heating system. In small towns, where other heat sources are unavailable, district heating centres produce only heat and are usually fuelled by wood, coal or oil.

While the initial investment in electric heating is low, electric heating consumes more energy than other methods. However, electric heating becomes more ecological with the use of green electricity.

© Heljo Juhani & Laine Hannele 2005. Sähkölämmitys ja lämpöpumput sähkönkäyttäjinä ja päästöjen aiheuttajina Suomessa - Näkökulma ja malli sähkönkäytön aiheuttamien CO2-ekv-päästöjen arviointia varten. Tampere 2005.

Figure 1. Finland's buildings by heating method in 2001 [1].

Where fuel is used, a boiler is installed and heat is produced by fossil or renewable fuels. Different fuels require different boilers and heat distribution systems. Oil used to be the most common fuel but following price fluctuations and a reputation for being non-ecological, it has lost its position in favour of wood, pellets and natural gas.

Heat pumps need electricity to work. Their efficiency is described by a coefficient of performance, which illustrates the ratio of heat produced to the electricity consumed. In Finland, coefficients of 2–2.5 are typical. Compared to direct electric heating, air source heat pumps that transfer heat into water can save 40%–60% in heating energy costs. Air source heat pumps that recover heat from exhaust air produce a saving of around 40% and ground source heat pumps a saving of 60%–70%.

In recent years, electric heating has lost some of its market share to ground source heat pumps and exhaust air heat pumps, while oil heating now holds a very insignificant share of the market.

Emissions from heating buildings

Emissions from heating buildings account for approximately 30% of Finland's total emissions (Figure 2). Heating is the largest single consumer of energy in households. Approximately 30% of Finland's total emissions are produced by housing, of which home heating accounts for 50% and water heating for 20%.

© Heljo Juhani, Nippala Eero & Nuuttila Harri 2005. Rakennusten energiankulutus ja CO2-ekv- päästöt Suomessa – Ympäristöklusterin tutkimusohjelma Rakennuskannan ekotehokkaampi energiankäyttö (EKOREM) -projekti, Loppuraportti. Tampere 2005. http://www.tut.fi/units/rak/rtt/tutkimus/ekorem/EKOREM_Loppuraportti_051214.pdf

Figure 2. Finland's estimated greenhouse gas emissions and their distribution in 2003. Building heating accounts for 26% or 22.3 Mt CO₂ eqv [2].

Reducing heating emissions

The simplest method of saving heating energy is to lower the indoor temperature. Temperature in residential and office buildings should be maintained at 20–22 °C. Storage buildings and similar can have lower temperature settings. Careful adjustment of temperature makes a difference: a change of one degree in the indoor temperature can represent a 5% change in the heating energy requirement. Premises should not consume a disproportionate amount of energy in proportion to their utilisation rate. Water heating represents approximately 20% of the total heating costs. Avoiding long hot showers and baths saves heating energy.

Insulation is another important energy saving method. The key points to consider include special materials, insulation thickness, and windows and other potential areas for leaks. In old buildings, as much energy can be lost through windows, replacing old windows with multiple glazing can become a viable option.

Air source heat pumps are an efficient means of reducing energy consumption in detached and semi-detached homes. The pumps cost relatively little (1,200–3,500 euros installed) and pay themselves back as energy savings. Typical savings in heating energy total 30%–40%. Using the fireplace to provide extra heat in winter is another efficient way of saving energy in any home, whether or not equipped with an air source heat pump. Better ventilation and heat recovery from exhaust air considerably improve energy efficiency but the initial investment can be high. Replacing the entire heating system, for example from oil to ground source heat, also carries high initial costs.

A number of comprehensive solutions are available for improving energy efficiency in new-build homes (Table 1). Particular attention should be paid to insulation and efficient ventilation systems, which recover heat from exhaust air. A low-energy house typically consumes 50% less heating energy than an average detached home. After insulation, the heating system is the largest single factor affecting emissions.

Table 1. The emission coefficient of various heating methods [3], [1]. The emission coefficient helps to calculate greenhouse gas emissions from heating.

During their lifetime, trees absorb as much carbon dioxide as they release when burned. However, it is worth paying attention to the quality of firewood and pellets because it affects fine particle emissions. The heat source with the second lowest emissions is ground source heat, but it is mainly suited to buildings in rural areas. It is always worth considering if the initial investment does not seem too high.

In urban areas, the most financially advantageous solution is the CHP district heating, as its energy efficiency can be improved by using landfill gas and surplus heat from industrial plants. In the review looking at average values, the emission coefficient of electricity is slightly smaller than that of district heating but, in practice, emissions from electricity use increase to a considerable level during cold spells. This creates an energy consumption spike, which is problematic in terms of electricity production. Therefore, emissions from electric heating are usually calculated using the marginal coefficient, which is considerably larger. Heljo and Laine [1] have also included a sample value, 400kg CO₂/MWh, which takes into account fluctuations in electricity production in more detail. Exhaust air recovery and air-to-water heat pumps are good at reducing emissions. Their emissions depend on the amount and production method of electricity but they are invariably smaller than those of direct electric heating.

Emissions from non-CHP district heating vary a great deal according to the production method. If heat is largely produced as a by-product of industrial processes or by renewable energy sources, emissions will remain low. If fossil fuels are used, emissions will be high.

Figure 3 illustrates the potentials of different means of reducing heating energy consumption in detached houses. The figure shows that the largest annual savings in energy consumption are achieved by using ground source heat pumps or two air source heat pumps, followed by heat recovery from exhaust air or exhaust air heat pump. Extra wall insulation (150mm -> 200mm) can provide savings of approximately 3,100 kWh/a but with high costs. Consequently, additional insulation is a viable solution only if carried out in conjunction with other renovation jobs. However, extra loft insulation (200mm -> 500mm) is a cost-effective measure, together with replacing incandescent and halogen lamps with compact fluorescent lamps (CFLs). Replacement windows (U factor 2 -> 0.8) become relatively expensive but, on the other hand, they improve living conditions by reducing draughts.

Figure 3. Investment costs of the measures to save in heating energy (€) and annual energy savings (kWh/a) [4].

How can municipalities make a difference?

Municipalities can reduce emissions from heating by disseminating information to their residents about energy saving opportunities, ensuring that energy-efficiency criteria is applied to the heating of municipal buildings and to new-builds and renovation projects, and attracting businesses that produce renewable energy in the municipality. 

Detached houses have the greatest energy saving potential in comparison with all other building types. For example, in the five small municipalities included in Rinne's [4] study, detached and semi-detached houses accounted for 43% of the total energy saving potential found in the municipality's buildings. Consequently, municipalities have the important task of disseminating information to their residents about the opportunities and positive outcomes of saving heating energy. Information should cover the opportunities to influence household heating costs (adjusting temperature settings, warm water usage, air source heat pumps etc.) and, at a more general level, the energy efficient heating choices (ground source, wood/pellets, district heating). Any special measures that the municipality might have implemented, such as a low-emission non-CHP district heating plant, are worth mentioning.

Municipalities should give a good example by maintaining appropriate temperatures in their own buildings and avoiding unnecessary heating of empty or little used buildings. Other measures include ensuring full occupancy of municipal office premises, favouring low-energy solutions in new-builds, and careful planning of building heating with special attention to environmental aspects. In renovation projects, insulation and replacement windows should be considered.