3.2 E NERGY SAVING MEASURES
4.1.2 Method for whole building renovation
A method was developed to conduct a component-based economical optimisation of the whole building, Paper III. The method originated from the method for new buildings presented by Petersen and Svendsen (2012). The developed method was adjusted and expanded to evaluate whether to execute the optimised renovation or to demolish the building and erect a new. Figure 4.3 shows the framework of the developed method.
Figure 4.3: The developed method for whole building renovation.
Step 1: Determination of cost of conserved energy
The marginal cost of conserved energy, CCE is calculated according to Eq. 4.1 for the different types and amounts or components of energy saving measure.
r measure year operation energy type
where, t is a reference period defined as the ratio between the reference period, nr
(years), and the useful life time, nu (years), and enables a comparison of measures
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interest rate (absolute number); Imeasure (€) is the marginal investment cost; ΔMyear (€) is the increase in annual maintenance cost; ΔEoperation (kWh) is the increase in annual energy use for operating the measure; EPenergy type (€/kWh) is the energy price for the operational energy; and ΔEyear (kWh) is the marginal annual energy saved by the measure.
For each type of energy saving measures, the energy usage can be expressed as a function of CCE based on the calculated CCE at different amounts, as illustrated in Figure 4.4. The amounts or components are the variation within an energy saving measures such as insulation thickness or different window components. Furthermore, for continuous measures different products can be assessed as shown in Figure 4.4a, this, however, is already included in the assessment of discrete measures e.g.
windows, see Figure 4.4b.
Figure 4.4: Examples of CCE curves for a) continuous measures and b) discrete measures.
In building renovation projects the first reference of energy saving measure is the existing structure or component. The marginal consideration of the energy saving measures implies that the reference structure must be considered as it was new. In case, the existing component is worn down, the component must be refurbished, thus the energy properties correspond to a similar new component. The refurbishment cost and energy usage of the reference component form the basis for the marginal CCE.
The concept of marginal CCE facilitates a direct comparison of the energy saving measures with respect to type. For example, CCE can be used to determine whether it is more efficient to insulate the roof or to choose a better window component. The one measure with the lowest CCE should be chosen.
The concept is easily applicable to continuous energy saving measures such as insulation materials. However, the concept of marginal CCE is more difficult to apply to discrete energy saving measures because they not necessarily are of the same component. In (Petersen, Svendsen 2012), a four step process is described how discrete energy saving measure can be converted into a continuous approach. An outline of the four step process is provided in the following:
1. The measures are listed with their investment cost and annual energy use. The measure with the lowest cost is chosen as reference. Typically, the existing component has the lowest cost. The cost of the existing measure is the needed
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refurbishment implying that the energy performance of the measure becomes as it was new.
2. The CCE for each measure is calculated with respect to the reference component as determined in step 1. Measures having a negative CCE are excluded. These measures are more expensive and use more energy than the reference. Thus they will never become economically efficient.
3. The smallest positive CCE derived in step 2 is set as the new reference.
Measures with an energy use equal to or higher than the new reference are excluded as they are not energy saving measures. Step 2 and 3 are repeated as long as there are measures.
4. The marginal CCE for all energy saving measures are calculated starting with the reference found in step 1.
Step 2: Optimising combination of energy saving measures
The second step of the method is an optimisation of a combination of energy saving measures for renovated buildings. The optimisation is defined as the energy-weighted average marginal CCE of the measures, herein called CCEaverage, equal to the energy price.
For discrete energy saving measures it is infrequent to obtain CCE values equal to the energy price. Thus the discrete measures must be chosen as close to the energy price as possible. This implies that the choice of continuous measures is related to the adjustment of CCEaverage to obtain CCEaverage equal to the energy price, as formulated in Eq. 4.2. Some energy saving measures in CCEaverage will be cost efficient and others not. This is acceptable when the combination of energy saving measures is
where, En is the energy consumption for the energy saving measure (kWh), CCEn is the cost of conserved energy for the energy saving measure (€/kWh), ΔEi is the sum of the energy consumption of all energy saving measures (kWh), and EPheat is the energy price for heating (€/kWh).
Step 3: Overall economy evaluation
The third step of the method is the decision whether to execute the optimised building renovation or to demolish the building and erect a new. The cost of an optimised combination of energy saving measures is to be compared to the cost of demolishing the building and erecting a new one. The method includes the cost of maintenance and operation for the expected service life of the building. Furthermore, it is possible to include the cost for improvements of the building such as new bathrooms and kitchens in the method.
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The building project to undertake is the one having the highest overall economic benefit as calculated in Eq. 4.3; hence the largest profit to the building owner at a potential sale of the building.
r
M & O
OE MV I D
a( n ,d ) (Eq. 4.3)
where, OE is the overall economic benefit (€); MV is the market value (€) for the renovated building or a new erected building; I is investment cost for energy saving measures, refurbishment, and building improvements, such as new kitchens and bathrooms (€); D is the cost for demolishing the building; M&O is the maintenance and operational cost discounted back to present value; a(nr,d) is defined as in Eq. 4.1.
Application of method on Ryesgade case
The developed method was applied to the Ryesgade case. The used constraint are the present energy price for heating (85.70 €/MWh), and a forecasted energy price for heating solely based on renewable energy (148.70 €/MWh), Paper III. Furthermore, the optimised combination of renovation measures was investigated with respect to two real interest rates. Figure 4.5 shows the energy consumption calculated based on the four scenarios of the economical optimised renovation. The transmission loss through the building envelope excluding windows and doors ranged from 11.5 to 14.5 W/m2 building envelope
Figure 4.5: Energy consumption for optimised Ryesgade case using different energy prices and real interest rates.
The overall economy was for the four optimised renovation scenarios calculated to about 2350 €/m2 heated floor area, whereas for replacing the existing building with a new the overall economy was calculated to about 1700 €/m2.
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4.2 Energy saving measures
In Figure 4.6 two energy saving measures are shown regarding solid masonry walls with embedded wooden beams.
Figure 4.6: Detailed description of the beam end and wall joint. The vapour barrier is placed between the gypsum board and mineral wool. a) The measure without a gap and b) the applied insulation with a gap.