The site is located in the western part of the city of Sofia in the residential area "Ovtcha Kupel". The area consists of large -panel apartment buildings varying from 4 to 8-story with adjacent kindergardens, schools and supermarkets. The selected apartment building was constructed in the 1980s. It is a four story, two-sectional block surrounded by roads and similar apartment buildings to the north and west and a kindergarden to the east. Sofia is located within the LT Climatic Zone area "Central". The building has a "high" exposure.
The complex is typical of Bulgarian mass residential building of 1970s and 1980s with prefabricated walls, floors and roofs. Longitudinal bays are 3.6 m wide. The external walls are constructed of prefabricated light concrete panels with 200 mm thickness on the elevations and 260 mm on the blank walls. The internal load bearing walls are of 140 mm thick prefabricated concrete panels. Internal non load bearing walls are 60 mm thick. The floors are constructed of 140 mm thick prefabricated concrete slabs with 30 mm screed. The roof is constructed of two 100 mm thick concrete panels with a 1010 mm inaccessible void between. The inner reinforced panel has a bad executed thermal insulation above the slab. The outer reinforced concrete panel has a weatherproof covering. Double glazed windows with a gap of 24 mm are constructed of timber frames cast into the reinforced concrete wall panels. The average U-value of the whole building is 2,16 W/m2K.
Central heating and hot water are provided from the district heating scheme with a vertical pipe net.
Problems
In Bulgaria most apartments are owned by the occupants. This together with the legal and economic position has inhibited action to resolve the problems of the buildings.
This project shows how an energy efficient refurbishment project could be self financed and could demonstrate the potential for improvement. This would encourage wider adoption of energy efficiency measures.
We believe that refurbishment of these buildings will extend the life of the buildings and improve the comfort of occupants. Monitoring of the antiseismic joints is to be carried out before the refurbishment.
The following pilot-project seeks to display some real proposals for refurbishment of a 4-story large-panel building. An execution of the project will show many advantages of the undertaken measures, but up to now , because of the legal and economical situation in the state, there is no motivation for the inhabitants, which are owners as well, to become enterprisers of such a refurbishment.
The project offers a new refurbishment way from economical point of view. A normal and an attic story, will be added to 4-story large panel building. This has been assessed from a structural point of view and is allowed according to Bulgarian codes. The project shows two variants for this construction. The first one, with a sloping roof is more traditional. The second one, with a roundshaped roof and rounded corners, is more economical in the sense that they reduce cooling effects.
The overcladding and refurbishment works of the existing building would be financed through selling the new apartments and ateliers. The addition of superstructure can resolve not only economic, but other problems as well. Replacing the existing flat roof with a sloping (or rounshaped) roof will avoid the annually repair of the waterproof insulation. The aesthetic quality of the building will also to be improved. The second variant provides an additional bufferspace to the south, which achieves better architectural view , a new comfortable extra- space for the apartments and an opportunity for solar gain.
New flats and ateliers will be constructed under a new span roof. Replacement of flat roof, with a bad waterproof insulation, with a sloping (or roundshaped) roof and avoiding the annual roofrepairs. Insulation of the roof with 100 mm mineral wool according to the Bulgarian building standard with a U - value of 0,53 W/m2K.
The existing windows and doors will be replaced with double glazed thermo-panes. The facades and the gables will be insulated with 100 mm mineral woolplates, fixed with metal screws. The joints between panels will be covered by the new insulation shell and will solve the problems of cooling and water penetration. The insulation will be covered with a new weather protection layer of render. The new U-value will be 0,495W/m2K. The south blank walls could be provided with photovoltaics panels. Floor over basement is insulated with 80 mm mineral wool plates. The second variant provides a replacement of existing south balconies with solar buffer spaces, which will allow passive solar gain.
It is planned to equip the existing vertical pipe system with by-passes and regulating valves. The substation will be equipped with electronic pressure difference regulator and meters. Each flat will be provided with heat allocation meters.
The installation of insulation will reduce the heat losses through the envelope significantly. The U-value for the whole building will be reduced from 2,16 to 0,84 W/m2K for the first variant and from 2,16 to 0,683 W/m2K for the second. The enclosed worksheets of LT4 method display the thermal behavior of the building before and after refurbishment for the first and second variant.
The mechanism of energy use in buildings is complex, involving three main factors; the physical building itself, the efficiency of the energy using equipment such as heating plant and lighting, and the way that the occupants control the building and the systems. Different combinations of these factors lead to a wide variance in energy use. Different combinations of these factors lead to a wide variance in energy use. For example, poor fabric insulation, an inefficient boiler, and occupants controlling excess heat by opening windows, will all contribute to very high energy use.
Refurbishment provides the opportunity to directly improve the building fabric and the systems, and these improvements may promote better occupant performance. For example, the fitting of room thermostats would remove the need for occupants to open widows to control overheating in winter. In developing a strategy, it is useful to be able to rank the impact of various measures. Savings are not simply additive - for example the value of heating energy saved by applying insulation would be greater for a district heating system of inherently low efficiency, than it would be for a building with its own high efficiency boiler.
The LT METHOD 4 is a design tool for use when establishing a strategy for energy conservation. Its main value is for making comparisons between various refurbishment options. The LT Method 4 responds to the following:
Clearly the first two factors are given constraints. The remaining ones all provide possible subjects for improvement as part of refurbishment. LT4 is a manual method. By means of pre-calculated graphs the user performs a sequence of estimations as follows-
LT 4 has an output in the form of annual energy use per square meter floor area. This is to allow comparison between the building under consideration and target values which are independent of the building size. Clearly it is a simple matter to convert this output to a total energy consumption value for a particular building by multiplying by the total floor area. The graphs are presented as a LT 4 Worksheet.
Heating energy is influenced primarily by winter temperatures, represented by heating degree - days, and secondarily by the availability of solar radiation. These two climatic variables are used to characterize three climate zones. The town of Sofia is in Central Continental zone with cold winters, between 2500 and 3500 degree days and moderate solar radiation.
The energy consumption per square meter is dependent upon the ratio of envelope surface area to building volume, or surface area to floor area. Energy consumption is quite sensitive in this ratio. Orientation of the building influences the distribution of glassing with respect to south, the direction from which most useful solar gains will be made in winter.
The conductive losses are controlled primarily by the thermal conductance of the opaque wall and roof, the thermal conductance of the glassing, and the glassing ratio - the ratio of the area of glass to the total wall area (including the glass and framing)
For calculating fabric loss, curves for three levels of wall insulation are proved corresponding to (a) uninsulated, U-value = 2.0, (b) low insulation U - value = 1.0, (c) high insulation U-value = 0.5. It is quite easy to interpolate or extrapolate the curves for other values. Three glassing types are assumed; single glassing U-value =5,5, double glassing U-value =3, triple or low-e glassing U-value = 2.
Infiltration is the ingress of air from the outside through the fabric, through cracks around windows and doors. Cracks can also exist between components such as door and window frames and the wall in which they are located, and between components such as floors, faces and soffits. Infiltration between components is particularly prevalent in prefabricated and partially pre-fabricated systems. Infiltration ( and intentional ventilation) constitute a heat loss due to the demand for heat to bring the incoming air up to room temperature.
It is generally agreed that for domestic activities ventilation rates of between 0.5 ac/h and 1.0 ac/h are sufficient, the lower values assuming that sources of heavy domestic pollution such as cooking and clothes-drying are ventilated locally. However, in many buildings, even the infiltration through unintentional openings such as the cracks described above, may lead to air change rates as high as 3 ac/h, in winter when the driving forces of wind and temperature difference are at their greatest.
This over-ventilation is wasteful of heating energy, and the reduction of uncontrolled ventilation(infiltration) during the general upgrading of the fabric is a valuable re-furbishment option. It can be achieved by weather sripping of openable doors and windows, re-caulking construction jots, or as part of over-cladding.
The distribution of the glazing with respect to orientation influences the availability of useful solar gains. The parameter used to estimate this is the ratio of the area of south-facing glazing to the total floor area. within the accuracy of the method, southfacing can be taken as any glazing facing within 45 of south. Orientation will also be relevant when estimating overheating probability.
The effect of solar gains is estimated using the second LT4 curve. These curves are provided for the particular climate zone and take account of the fraction of solar gain which is useful in displacing auxiliary heating. The curves also include the effect of internal gains from people, lighting and equipment. The presence of thermal mass increases the usefulness of solar gains by storing them and reducing the risk of overheating. The data for the curves is generated by the mathematical model, assuming a medium to heavyweight building construction. In the less common case of a light-weight-building, or a building lined with light-weight insulation and light-weight partitions where all the thermal mass is isolated, the solar contribution should be reduced by about 30%. It is also important to note that the solar energy will only reduce auxiliary heating if the control system can respond. The curves also include the effect of internal gains from people, lighting and equipment. The presence of thermal mass increases the usefulness of solar gains by storing them and reducing the risk of overheating. The data for the curves is generated by mathematical model, assuming a medium to heavyweight building construction. In the less common case of a lightweight building, or a building lined with lightweight insulation and lightweight partitions where all the thermal mass isolated, the solar contributions should be reduced by about 30%. It also important note that the solar energy will only reduce auxiliary heating if the control system can respond.
Sunspaces and atria (referred to generically as buffer spaces) do not have auxiliary heating themselves and reduce heat losses from the spaces to which they are attached by reducing conductive losses through the wall of the heated building, and possibly by providing some ventilation air at a higher temperature than ambient air( often referred to as ventilation preheating). Both of these effects occur due to heat from the heated building raising the temperature of the unheated bufferspace and are further enhanced by solar gains made in the bufferspace. Ventilation pre-heating will only take place if flow paths are designed to encourage airflow from the buffer space to the heated interior.
In LT4 the contribution that the buffer space makes is given in the form of annual saving per square meter of separating wall. The separating wall is the area of wall between the heated building and the unheated bufferspace. The saving will also depend on the conductance of the separating wall which is influenced by the level of insulation and the amount of glazing. Values are given for south-facing buffer only, south-facing with ventilation pre-heating, and non-south-facing buffer spaces only. Three different configurations are identified. The first is where the buffer space is formed by, in effect, glazing over all or part of the south facade to form individual bufferspaces i.e. there is only south facing vertical glazing. This could bee realized by glazing in access galleries or balconies, or providing a "second skin" of glazing to the facade. The second two cases relate to an atrium configuration, where there is a significant amount of roof glazing. One case is where a large glazed space is attached to the side of a building. The other case is where the space between two buildings is roofed over.
Values of thermal savings are given in Table 2 for the three climate zones.
The factors discussed above influence the demand for useful heat. Two further factors relate to the amount of energy delivered to the site in the form of fuel, the wastage of heat in its distribution to the point of use(the rooms) and the efficiency with which the fuel is converted into heat. In some cases, residential buildings may be heated by waste heat from power stations (Combined Heat Power) in which case the efficiency of the initial conversion of fuel to heat becomes less important, provided there is sufficient heat available. System efficiencies can be estimated from Table 3 below. To allow inter-comparisons between types of fuel, and to make direct comparisons with electricity use, the final output is in primary energy. This is the energy value of the fuel plus the energy overheads involved in bringing it to the site and relates well to the cost and to the environmental impact due to CO2 production and other pollutants.
For most true fuels, the energy overhead is small, but in the case of electricity, for thermodynamic reasons, there is a very large energy overhead when fuel is converted into heat, mechanical and finally electrical power. Typical delivered to primary energy ratios for electricity are around 30%. This makes an overwhelming case for not using electricity for heating. Even when electricity comes from a renewable source such as wind-power or hydro, it can be argued that since Europe has an electricity supply grid, this "clean" power should be used to displace conventionally generated power.
The worksheet is a series of charts organized so that outputs from one chart can be transferred graphically as an input to the next chart. The steps in using the Worksheet are as follows, using data from the existing building to establish the base case.
The appropriate worksheet for climate zone and building form has to be selected - i.e. surface area to volume ratio(total surface area includes groundfloor, walls and roof).
A few key parameters of the building have to be calculated from the drawings or building descriptions. these are-
These values are used to calculate the ratio G/W which is used to calculate the fabric losses, and S/F which is used to estimate the solar gains. If there is a buffer space, the area of separating wall(between the buffer space and the heated building) also has to be specified
This value is used to calculate ratio B/F which is used to estimate the energy saving due to the buffer space.
On chart A with the approximate glazing ratio G/W on the vertical axis has to be drawn a line across to the appropriate curve. They are grouped into good, medium and poor levels of insulation, each group has curves for single, double and triple or low-E glazing. If the standard values are unsuitable then has to be interpolate or extrapolate. From the point of intersection the value with a vertical line is transferred to chart B. The annual heating energy in KWH/m2 (primary energy units) for the conductive losses, is shown where the vertical line crosses the horizontal axis at the bottom of chart A.
By reference to Table 1 or other information has to be used scale B1 to evaluate infiltration heat losses and this has to be added to at the top line of chart B by moving horizontally to the right. It has to be interpolated or extrapolated if necessary. This value has to be transferred with a vertical line down to chart C.
From the value of south glassing area to floor area ratio S/F, has to be chosen the appropriate curve on chart C, or interpolated. If a building has no south - facing glazing, it has to be used the 0% curve; this will account for the effect of useful internal gains only. From the point of intersection with the appropriate line the value has to be transferred to chart D.
If there is a buffer space thermal saving has to be determined from Table 2 and deducted from the current energy value in the left hand column of chart D, in a similar way to the infiltration energy at chart B, but on the vertical axis.
It has to be determined the heating system efficiency by reference to Table 3 or other sources and the value has to be transferred from chart C or D to the appropriate curve. From the point of intersection has to be transferred the value upward to chart F.
The bar chart has to be drawn for the base case. Conductive, infiltration and buffer space components could be presented separately as stacked bars. There is a scale change at chart E.
The proposed refurbishment options can now be evaluated in a similar way and there is room for three options to be displayed alongside the base case. The options can be described briefly in the box at the left of the bar chart.