Methodology: Demand Reduction

The EDEM program, developed by the ESRU department at the University of Strathclyde, was used to model changes made in the dwellings and their expected impact on energy consumption and CO2 emissions.  This program was designed primarily to deal with dwellings so was the perfect to use for the project’s modelling purposes for domestic demand reduction.   The program has a spreadsheet type interface and a number of changes can be made to the dwelling, with emphasis put on fabric determinate schemes and boiler changes for this project.  It was agreed that these would be the two areas that should be concentrated on as it has the biggest impact on CO2 emissions.

Modelling Procedure

The modelling was based on predefined models in the EDEM database for different types of dwelling, such as 3 storey pre-1981 flat or detached house.  The models make a number of assumptions about the original design and construction of the dwellings such as their likely levels of insulation or boiler types.  To start off the modelling, the worst case scenario for all the dwellings was modelled.  This is to say that it is assumed the fabric and boiler had not been changed since being installed when the building was built. Obviously, this would not be the case in real life, so a second, more realistic, base case was created with data kindly provided by Milnbank housing association in the area.  This second base case was verified with the gas and electricity consumption for the area obtained from the IGZ data for the project area.

Table 1 illustrates the differences between the two base cases used in the modelling of the various dwellings.  It can be deduced from these values that both cases have no differences between insulation installed in the floor or the glazing, which is single glazed.  The second base case has cavity wall insulation and has 50mm of loft insulation put in compared to the initial base.  For both base cases it is assumed that the airtightness in the dwellings is poor.  All the fabric determinate schemes and their corresponding U-values can be found on a spreadsheet on the downloads page.

 

Base Case 1

Base Case 2

Fabric Determinate Scheme

Poor

Standard

Boiler Type

Low Efficiency

Medium Efficiency

U value wall

1.7

0.6

U value roof

0.96

0.45

U value floor

0.7

0.7

U value glazing/door

5

5

Table 1: Differences of the two base cases used for the modelling

Boiler changes sensitivity study

Table 2 shows the expected carbon savings as a percentage that could be saved per annum, regardless of the insulation scheme.  The table also shows that there is not a large difference in total costs of the three different boiler upgrades.  These values hold true for all the types of dwellings that exists in the project’s location of interest. The boiler changes are inclusive of heating control upgrades and installation costs. 

Boiler type

Carbon footprint saving

Cost from low base (£)

Low efficiency

0%

0

Medium efficiency

~10%

1520

High efficiency

~20%

1600

Gas condensing

~30%

2000

Table 2: Summary of results found in sensitivity assessment of boiler changes

The two base cases that are being looked at in this project had different boilers in their setups.  The first base case was assumed to have a low efficiency boiler while the second, more realistic base was assumed to have a medium efficiency boiler.

Investigations found that changing the boiler was one of the most cost effective methods of reducing the annual carbon footprint of a dwelling.  As the differences in costs between the different boilers are not large, the gas condensing boiler would be part of the recommended dwellings improvements scheme.

Fabric changes sensitivity study

The next step was to see which fabric determinate scheme would be the best match the boiler changes.  Each type of dwelling was modelled with each available insulation scheme.  Table 3 shows the available schemes for insulation improvement.

Insulation Scheme

Details

Poor (pre 1983)

Insulation standards applied representing building standards prior to the 1981 Scottish building regulations.

Standard (1983-2002)

Insulation standards applied representing building standards defined by the 1981 Scottish building regulations.

Medium (2003-2007)

Insulation standards applied representing building standards defined by the 2002 Scottish building regulations.

Good (post 2007)

Insulation standards applied representing building standards defined by the 2007 Scottish building regulations.

Super

Insulation standards applied representing building standards defined by the AECB ‘Gold’ and ‘Passivhaus’ guidelines.

Table 3: Possible insulation schemes for improvements on dwellings. Taken from EDEM manual

Results

Two sets of recommendations have been made; the first case is to look at the best scheme to identify the optimum possible carbon savings could be achieved when there are no financial restraints.  This best scheme is made up of super insulation scheme combined with a gas condensing boiler.  The second scheme is a more realistic scheme where the economic side is taken into account.  Here the scheme has to provide a good balance of large energy savings while keeping costs down as much as possible.  The ideal realistic scheme should include a gas condensing boiler, as mentioned in the boiler analysis.

A sensitivity assessment was carried out to establish which insulation scheme ties in best with the gas condensing boiler for the realistic improvement scheme.  Figure 1 shows potential carbon savings with each insulation scheme for a ground floor tenement flat.  It can be seen that the most significant savings are made when going from the standard to the medium insulation scheme, compared to the savings made from moving to the good and super insulation schemes.  The super insulation scheme can be neglected for the realistic case as it is simply too expensive in comparison to the benefits gained.  The good insulation scheme also does not show a significant difference of savings for the amount of monetary input compared to the medium fabric determinate scheme.

An example of a sensitivity assessment for the various EDEM schemes for a ground floor tenement flat

Figure 1: An example of a sensitivity assessment for the various EDEM schemes for a ground floor tenement flat

It was therefore deduced that the most realistic scheme would be a gas condensing boiler and with the medium insulation scheme.

References