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Analysis of an example energy rehabilitation of a building according to the state plan 2013 - 2016
In this article we will describe a example of energy rehabilitation which is included in the presentations and talks that are part of the 1st Biennial of Sustainable Building and Urbanism, specifically the one corresponding to a pilot case in the road neighborhoods of Cádiz in Malaga.
The following case study was carried out by Fernando Gutiérrez Garrido together with Daniel Rincón de la Vega, a few years ago at the Greencities Congress.
Characteristics of the performance (Building):
The building corresponds to a block of 34 Limited Rent homes with commercial ground floor, located in the street of Héroes de Sostoa and Velasco in Málaga. The building has two facades facing Northeast to Velasco Street and Southwest to the rear. It has a total of 10 floors of flats with two typologies that are maintained in levels 1 to 4 and in levels 5 to 10.
The distribution of the houses corresponds to the usual one of that time with three and four bedrooms, a bathroom, kitchen, laundry room and living-dining room, and their shape and distribution make it difficult to properly cross-ventilate them. It has a foundation and structure made of reinforced concrete.
Thermal envelope of the building:
The exterior facades have a total thickness of 25 cm, and present a composition from the outside to the inside made up of a hollow brick partition, chamber and hollow brick partition, with an exterior finish by plastering and painting.
It presents a roof resolved with partitions on the slab of the last floor, on which supports a rasilla board finished with compression layer and Arabic tile. Presents metallic exterior carpentry and has roller blinds. It has double glass as indicated in the specification, but the thickness is not defined.
Calculation procedure and hypothesis: Proposal for improvement.
To model the building, the CALENER VYP program has been used, with which the demands and energy consumption for heating and cooling as well as CO2 emissions are obtained.
A simulation of the building in its current state has been proposed to know the energy demands and consumption, and thus analyze the possible improvement actions for the rehabilitation of the building. Thus, three actions are proposed to reduce demand and another to reduce non-renewable energy consumption, being the following:
- Action D1: Increase in the level of insulation on the facades of the building.
- Action D2: Replacement of carpentry and glass.
- Action D3: Increased level of insulation on the roof of the building.14
- Action S1: Incorporation of solar collection for ACS and replacement of support equipment and type of energy.
Results obtained:
Action D1. Increase in the level of insulation of the facades.
In this first example of energy rehabilitation, it is taken into account that the thermal transmittance value is higher than that required by the Technical Code for the reference climatic zone (zone A3). To comply with the established requirements, it is necessary to increase the insulation so that its thermal resistance will be as follows:
[highlight] U [/ highlight] CTE: 0.94 W / m²K (R: 1.06 m²K / W)
[highlight] U [/ highlight] BUILDING: 1.40 W / m²K (R: 0.71 m²K / W)
[highlight] R [/ highlight] BUILDING + [highlight] R [/ highlight] THERMAL INSULATION REQUIRED = RCTE
[highlight] R [/ highlight] REQUIRED THERMAL INSULATION: 0.35 W / m²K
An extruded polystyrene with conductivity 0.038 W / mK is chosen, so that a sheathing is required on the outside with the following thickness:
e = R ∙ λ = 0.35 W / m²K x 0.038 W / mK = 0.0133 m = 1.33 cm
A cladding on the outside has been proposed, with an insulation thickness of 3.00 cm with an insulating material with a conductivity of 0.038 W / mK. So that the transmittance of the facade of the improved building will be:
[highlight] U [/ highlight] IMPROVED BUILDING: 0.66 W / m²K (R: 1.51 m²K / W)
With this scenario, the energy savings in energy demands and emissions are obtained, which are expressed in the following table:
Action D2: Replacement of carpentry and glass.
According to the construction solutions of the project, this presents metal windows without thermal break with double glazing, with the following characteristics:
Gap transmittance U: 5.60 W / m²K
Solar factor 0,68
The frame percentage is considered to be 18%, with an absorptivity of value 0.8 (dark frame) and glass solar factor of value 0.80. The gap percentages in each orientation are as follows:
- North: 16%
- E: 22%
- Or: 21%
- S: 31%
The thermal transmittance of the holes, for each orientation presents the following deviation, with respect to the limit values:
- North: 0% (equal to limit transmittance)
- E: 12% lower
- Or: 12% lower
- S: 16% lower
It is proposed to replace carpentry and glass with others made of PVC and 4 + 9 + 6 double glass that comply with the minimums established in the CTE for each orientation.
[highlight] U [/ highlight]CTE: 2.86 W / m²K, FS CTE: 0,63
In this second case, the following energy savings are obtained:
Action D3: Increase the level of insulation on the roof of the building
In this case, the thermal transmittance of the roofs is 1.04 W / m²K, 108 higher.% to the limit value required by the basic document DB-HE for the reference climatic zone (zone A3). To strictly comply with the established requirements, an increase in the insulation level is required with the following value:
[highlight] U [/ highlight]CTE: 0.50 W / m²K (R: 2.00 m²K / W)
[highlight] U [/ highlight]BUILDING: 1.04 W / m²K (R: 0.96 m²K / W)
[highlight] R [/ highlight]BUILDING + [highlight] R [/ highlight]THERMAL INSULATION REQUIRED = RCTE
[highlight] R [/ highlight]THERMAL INSULATION REQUIRED: 1.04 W / m²K
An extruded polystyrene with conductivity 0.038 W / mK is chosen, so that a sheathing is needed on the outside with the following thickness:
e = R ∙ λ = 1.04 W / m²K x 0.038 W / mK = 0.03952 m = 3.95 cm
A cladding on the outside has been proposed, with an insulation thickness of 4.00 cm with an insulating material with a conductivity of 0.038 W / mK. So that the thermal transmittance of the roof of the improved building will be:
[highlight] U [/ highlight]IMPROVED BUILDING: 0.49 W / m²K (R: 2.04 m²K / W)
In this case, the following improvements are achieved with respect to the initial situation:
Action S1: Incorporation of collectors for DHW with centralized accumulation.
The incorporation of solar collectors for ACS on the roof is proposed, so that an installation with centralized accumulation and distributed support is generated that complies with the minimum solar contribution required in DB-HE4.
Climate zone: IV
Reference demand: 22 liters per person
Reference temperature: 60 ºC
Occupancy: 152 people
Total demand: 3344 liters
Supporting energy source: Natural gas
Proposed solar contribution: 70%
In the latter case of improvement, obviously the energy demand is maintained since the envelope is not acted upon, but it does improve energy consumption and emissions according to the following table:
Based on these four improvements, several scenarios are proposed in which these hypotheses are combined, obtaining the following savings with the investment costs and amortization periods indicated:
Investment proposal according to the state plan 2013 - 2013
It is based on the main criterion whose objective is to reduce energy demand by at least 30% in accordance with the specifications contained in article 20 of the Eligible Actions of the State Plan to promote housing rental, the building rehabilitation, and urban regeneration and renovation, 2013-2016. To do this, the chosen action must be modified until the energy demand in the building is reduced by an additional 3.19% over that produced by the chosen action. This is achieved by increasing the thickness of the exterior insulation proposed for the facades, so that the definitive intervention is the one specified:
- ACTION D1: With a 5 cm thick exterior cladding and [highlight] U [/ highlight]IMPROVED BUILDING: 0.50 W / m²K
- ACTION D2: Replacement of carpentry and glass with PVC windows and 4 + 9 + 6 glass with a [highlight] U [/ highlight]CTE: 2.86 W / m²K and FS CTE: 0.63.
- ACTION S1: Solar collectors are incorporated for DHW production with a system with centralized accumulation and distributed support, which complies with the minimum contribution required in the basic document DB-HE4, with a solar contribution of 70%.
With these new proposed actions, the intervention is eligible and although the cost of the investment is slightly higher than the initial one, the repayment period is reduced by one year.
Some of the most relevant conclusions of the study are the following:
The incorporation of thermal insulation in the facades of these Limited Rent buildings represent an economical, constructive and architecturally viable option to improve the thermal behavior of buildings.
With the replacement of carpentry and glass, a viable intervention is achieved both from the economic point of view and constructively speaking, being able to simultaneously improve other benefits of the building such as protection against noise and indoor air quality (with the incorporation, where appropriate , of aerators).
When it comes to improving by incorporating thermal insulation on the roof in blocks similar to the one analyzed, there is no significant reduction in demands, energy consumption and emissions.
Incorporating solar thermal energy through solar collectors is feasible in the case of comprehensive interventions, since the performance of the equipment and their number and arrangement can be optimized.
