Feasibility study of the insulation of the enclosing walls of high-rise buildings

On the example of a typical residential multi-apartment building, a feasibility study was carried out on the choice of energy-saving measures for the thermal insulation of facades. The decision to increase the energy efficiency of the building was made on the basis of calculating the loss of thermal energy through the external walls. Based on the parameters of the heating period, capital costs for additional thermal insulation of facades and calculated values of operating costs for heating, the optimum thickness of the additional layer of insulation is determined, in which the payback period assumes a minimum value.


Introduction
Reduction of energy costs is the most prospective area of resource saving in design and operation of buildings. Previous technical solutions to decrease the construction cost led to increase in cost of electricity [1].
In recent years, energy saving has become essential for new buildings and houses built several decades ago, when the issue of heat consumption was not considered.
Nowadays the state program about repair of old buildings is being implemented. It is necessary that it correlates with the energy saving program [2,[4][5][6][7]. At the same time, the economic component of investment projects should not be ignored. Energy-saving measures should reduce the amount of consumed energy and ought to be recoupable.

Thermotechnical calculations of enclosing structures
Let's make the analysis of choice of energy-saving measures for insulation of facades. The building is 9-storey building located in Saint-Petersburg. The total area of external enclosing structures is equalled to 5963.1 sq.m. The climatic conditions for residential buildings are presented in table1.
Thermotechnical calculation showed that thermal resistance of wall R0 = 0.97 m 2 ×°C/W is lower than the required value Rreq= 3.08 m 2 *°C/W. Due to identified discrepancy, it is necessary to insulate outer walls of construction object. Minimal value of allowable thermal resistance of the thermal insulation material: Nowadays there are many options for insulation. We will determine the required thickness of wall with ISOVER Warm walls insulation to provide the required thermal resistance of wall: Insulation ISOVER Warm walls is available in the form of plates with a thickness of 50 and 100 mm. Let's consider that the thickness of the insulation will be equal to 100 mm: According to the result, R0 = 3.75 m 2 *°C/W > Rreq0 = 3.08 m 2 *°C/W, the thickness of insulation is chosen right. The same calculations for other well-known insulations are given in table 3. Table 3. Technical assessment of insulation [8][9][10][11][12][13]. Insulation URSA Terra as the most low-cost insulation material which provides the biggest value of thermal resistance is chosen for insulation of facades (table 3).

Return on investment in insulation of facades
The equation (5) is used to calculate the discounted payback period of investments aimed at additional insulation of facades [14].
where discounted payback period of investments in years;

ΔKthe difference between the capital costs for the construction of insulated and basic variants of the exterior walls (facades) of the building, RUB;
ΔEthe difference between the loss of thermal energy through the outer walling before and after insulation, RUB; raverage increase of electricity pricing in %; i -discount rate in %. The optimal option for additional insulation of facades will be considered the one for which the payback period will be minimal, i.e. the condition [15,[17][18][19]: We will accept that building company took out a loan for 13.7% for 3 years (m = 36) for additional insulation. In this case, the annuity coefficient will be 0.034: where mduration of credit payment in months; monthly discount rate.
The annual saving, which is achieved because of works on renovation of facades of the existing building, is defined by the formula: Heat conductivity of outer walls without additional insulation: The required thermal resistance for the exterior walls of residential buildings due to the climatic conditions of Saint-Petersburg is equal to Rreq= 3.08 m 2 *°C / W, which corresponds to the heat conductivity V2: Electricity pricing has been increasing at 11.3 % per year for last 10 years (table 4). Thus, the average annual growth of pricing is equaled to 0.113 [20,21].

Conclusion
Energy-saving measures should be recoupable. Unfortunately, the problem of optimization of long-term investments in energy-saving measures in the construction and operation of buildings is rarely considered, especially using parametric models. In this article, the decision to improve the energy efficiency of residential building was made based on the calculation of heat losses through the outer walls. The optimal insulation thickness is determined due to the parameters of the heating period, capital costs for additional insulation and calculated operating costs and allowed to minimize the payback period.