Analysis of the thermal and technical parameters of the vegetated roof and its effect on the energy demand – Case study A

ENERGY!!! In this energy era, when the development of energies and the development of their prices is a daily topic that affects people’s lives, it is necessary to direct our thinking towards the reduction of global energy demands. In my industry, it’s reducing buildings’ energy needs, specifically for heating and cooling. It is known from many researches and studies how it is possible to reduce the energy demand of the building in the area of constructions by insulation, or suitable design of the envelope or in the area of Building services, by using renewable energy sources or by using a suitable source and type of heating and cooling. Therefore, I took a different direction in my research. PASSIVE COOLING. Passive so that we don’t fight against energy with energy, but that we use the amount of it that falls on the object in the largest possible amount and eliminate the rest with suitable design and suitable elements. I focus on VEGETATION and its potential in this direction. My work has several chapters, and in this article I am dealing with one of the first, namely the analysis of the thermal engineering parameters of the constructions in case study A.


Energy efficiency of building
The topic of global warming is more than actual these days.The media often reports on this problem and people actively perceive it.The weather itself is significantly affected by this phenomenon, and this has a great impact on the population.One of the main, if not the primary, impact of climate change is urbanization [1] -the movement and centralization of the population into cities.It is possible to monitor its increase in the long term, and forecasts do not indicate the opposite.Every year, this phenomenon has an upward trend in most states, although it fluctuates in some cases.Slovakia is an example of this.According to data from the study [2], the development of the urban way of life has the following values.In Fig. 1 according to [3] it can be seen that already in 2007 the world exceeded the level of urbanism by 50%.This trend has an impact on several aspects of the climate crisis.Therefore, we got into one big climatic chain.Urbanism causes an increase in the temperature of cities, thereby strengthening one of the significant problems of cities -UHI (Urban Heat Islands).It also increases the local need for energy for heating and cooling, and this means an increase in the production of greenhouse gas emissions.Today's goal is the exact opposite and the reduction of energy consumption.
This article is part of the research in my dissertation, where one of the main goals is to find ways in our climate to prevent the energy fight in buildings with additional energy as much as possible.Of course, it is not possible to completely eliminate it, but it is necessary to find ways to reduce it as much as possible.One of the options (in addition to proper architectural design, shielding, appropriate building envelope, etc.) is the use of passive heating and cooling elements.In my work, I focus on the application of vegetation elements and its effect on heating and cooling, specifically on the interior part.

Vegetation elements
Today, there is no doubt that vegetation elements, especially vegetation roofs, have many advantages, such as reducing rainwater runoff, enriching urban biodiversity, mitigating UHI, improving air quality, reducing thermal oscillation on the roof surface -extending the life of the roof membrane, reducing noise levels and reducing energy consumption.This article deals with the latter aspect [1].
During the summer season, due to the rising temperature in the exterior and subsequently in the interior, the demand for cooling increases.The calculated indoor temperature in Slovakia during the winter period is 20°C and 26°C in the summer.However, it is known that people often think the opposite.They require 20°C in summer and 24°C and more in winter.Therefore, the demand for heating and cooling is increasing.Since cooling is often provided by air conditioning units, this results in an increase in the exterior temperature, whether at the local or urban level, and subsequently supports the UHI issue.It is known that through evapotranspiration, a large amount of solar radiation can be converted into latent heat, which does not cause an increase in temperature [4].This is another reason to use passive cooling elements.
Why the roof?In our climate zone, it is problematic to maintain vegetated exterior facades.Also, these structures -horizontal building structures are exposed to high thermal stress during the summer season, and require significant measures to prevent heat loss in the winter season [5].
As the benefits are proven, some states have decided to include their applications in cities and support them.It was legally incorporated by Toronto in 2009 [6].Other cities, such as e.g., supported this issue.Chicago.

The influence of vegetation elements on heat flow and heat conductivity coefficient
Several factors affect how well the vegetation roof can meet the building's energy needs.Among them are the thickness and thermal conductivity of the substrate, volumetric humidity, height of vegetation, leaf efficiency, emissivity and their coverage, stomatal resistance -the product of linear discontinuous functions of leaf water potential and solar flux, as well as the type and thickness of the roof insulation and from the climatic climate [1].
As for the effect of the vegetated roof on the heat flow, or for the thermal and technical parameters of the roof, which I would use in energy balances, I drew from texts [5,7].This case study deals with the analysis during the heating period.
In the study [7], 3 types of roofs (differing in insulation thickness) were considered.For our climatic zone and our country, it is necessary to consider a well-insulated roof.
Table 2. Shows the values of the heat transfer coefficients of the given structures either with or without a vegetated roof for three levels of insulation [7].
1. uninsulated roof a. 25 cm concrete b. 10 cm concrete 2. slightly insulated roof a. 15 cm of concrete + 5 cm of insulation + 15 cm of concrete, b. 5 cm concrete + 5 cm insulation + 5 cm concrete 3. well-insulated roof a. 15 cm of concrete + 15 cm of insulation + 15 cm of concrete, b. 10 cm of concrete + 10 cm of insulation + 10 cm of concrete

Direction of research
The article captures case study A, where I chose to start with an unrealistic object of a warehouse-type hall with dimensions of 100x200x10m (width x length x height) -part A1.
In this case, the roof area makes up 43.48% of the building's heat exchange envelope.For the principle assessment, I considered roof 3a, which is the closest to our conditions.Subsequently, when choosing an object, or other buildings, it is necessary to consider the factor of the building's shape and thus the ratio of the individual areas of the building's envelope to the vegetation area.This article features a building with a large roof-to-wall ratio.For comparison, I added an apartment building with dimensions of 14.76x31.66x23.1m(width x length x height) -part A2, where the roof area is only 15.13% of the building area.In fig. 2 and 3 are the dimensions of the two compared objects.After selecting the object, the surfaces of the perimeter structures (floor, walls and roof) were compared.These relationships can be seen in table 3 and table 4. In part A1, a significant reduction in heat loss through the roof structure can be seen.This influence is also displayed in the overall balance of the object -Table 7. The balance of part A is shown in table 10.By transferring these values to the annual balance of energy needs for heating, we also get the value of savings in kWh/year or GJ/year.From this, when converted to current energy prices in this period, it is also possible to determine the total economic annual savings.Part A1 is captured by table 11-13 and part A2 table 14-16.A2, where you can see the difference in percentage savings with a vegetated roof, but also with different ratio of the area of the given roof.Therefore, the greater justification for the use of a vegetation roof, as far as heating is concerned, is for objects with a larger area of horizontal constructions compared to vertical ones.

Conclusion
Even the overall effect of the vegetation roof on the object depends on a number of factors, the result confirmed the effect on heating.At the same time, a secondary comparison based on the ratio proved its suitability for different area ratios.The subject of this article is not an economic principle, as it is not objective to compare one indicator and its financial side.On the other hand, this article is intended to enrich the view of vegetated roofs and to complement its advantages.
This work was supported by Development Agency under the contract (APVV APVV-18-0360 ACHIEve Active hybrid infrastructure for the sponge city).

Table 3 .
Area ratio of packaging structures -part A1.

Table 4 .
Area ratio of packaging structures -part A2.The thermal and technical parameters of the structures are the same for both parts, so that only the roof structures can be accurately compared.Part A1 is shown in table 5 and 6.Part A2 in table8 and 9.

Table 5 .
Calculation of heat losses by constructions without a vegetated roof -part A1.

Table 6 .
Calculation of heat losses by constructions without a vegetated roof -part A1.

Table 8 .
Calculation of heat losses by constructions without a vegetated roof -part A2.

Table 9 .
Calculation of heat losses by constructions without a vegetated roof -part A2.

Table 11 .
Annual energy requirement for heating without a vegetated roof -part A1.

Table 12 .
Annual energy requirement for heating with a vegetated roof -part A1.

Table 13 .
Total comparison of heating energy demand -part A1.

Table 14 .
Annual energy requirement for heating without a vegetated roof -part A2.

Table 15 .
Annual energy requirement for heating with a vegetated roof -part A2.

Table 16 .
Total comparison of heating energy demand -part A2.In the final table No. 3, you can see the overall comparison of parts A1 and

Table 17 .
Final comparison of constructions with and without a vegetation roof.