Building components with incorporated phase change materials (PCMs) meant to increase heat storage capacity and enable stabilization of interior buildings surface temperatures, whereby influencing the thermal comfort sensation and the stabilization of the interior ambient temperatures. The potential of advanced simulation tools to evaluate and optimize the usage of PCM in the control of indoor temperature, allowing for an improvement in the comfort conditions and/or in the cooling energy demand, was explored. This paper presents a numerical and sensitivity analysis of the enthalpy and melting temperature effect on the inside building comfort sensation potential of the plastering PCM.
Nanotechnology and nanoproducts offer interesting new opportunities in many civil engineering areas and architecture including design and construction processes, such as the development of novel insulation materials. These novel materials with very good insulation values are already available on the market, enable a thermal rehabilitation of buildings in which conventional insulation is not possible, and can help to improve energy efficiency. On the construction industry not all products that feature the term “nano” actually contain nanomaterials. Often, the term “nano” merely refers to structures in the nanosize range. Nanotechnology in the construction industry is currently concentrated in the following sectors: cement-bound construction materials, noise reduction and thermal insulation or temperature regulation, surface coatings to improve the functionality of various materials, fire protection.
This paper presents the application of nanotechnology, in the construction process, to improve the building energy efficiency. One of the greatest challenges in the construction sector is the thermal renovation of existing buildings; and applying new insulation materials based on nanotechnology could make an important contribution. In the past, energy consumption has increased steadily. However, the energy efficiency of buildings is today a prime objective for energy policy at regional, national, and international levels [
A PCM is a substance that changes from one state of matter to another at a certain temperature and represents a technology that may reduce peak loads and HVAC energy consumption in buildings. Building materials with incorporated PCM are meant to increase heat storage capacity and enable stabilization of building interior surface temperature, whereby influencing the thermal comfort sensation and the stabilization of the interior ambient temperatures [
Thermal energy storage based on the latent heat of phase change material has attracted attention of researchers and engineers in different fields, and a considerable number of numerical researches on PCMs have attempted to estimate potential energy savings through building energy simulation. To analyse energy and peak load benefits from PCMs a significant number of commercial building energy simulation programs such as CoDyBa, EnergyPlus, ESP-r, and TRNSYS were used.
EnergyPlus PCM algorithm uses a one-dimensional conduction finite difference solution algorithm (CondFD). This algorithm was tested and validated against multiple tests suites [
As far as the organization of this paper is concerned, Sections
Thermal comfort of interior building spaces can be achieved using sensible heat form, related to conventional building materials, or via latent heat form, associated with PCMs. PCMs used for latent heat storage in buildings are characterized by an endothermic behaviour (with energy accumulation) during solid-liquid transition and exothermal process (with energy liberation) during liquid-solid phase shift. The solid-liquid PCM group comprises three categories: organic PCMs (paraffins and fatty acids); inorganic PCMs (salt hydrates and metallics); and eutectic mixtures (organic-organic, organic-inorganic, and inorganic-inorganic).
Thermal properties, like melting temperature and phase change enthalpy, are crucial to the process of selecting a suitable PCM for thermal energy storage. The scheme shown in Figure
Melting temperatures and phase change enthalpy for existing PCMs (adapted from [
Salt hydrates and eutectic mixtures present the highest phase change enthalpy for the operative temperatures required inside building spaces. However, the set of characteristics presented by paraffins makes of these the most desirable materials to be used in latent heat storage systems. Organic materials, such as paraffins, are chemically stable, offer no supercooling, and are available in a large temperature range with low cost.
Phase change materials can be incorporated into conventional construction materials mainly by three different technics: direct incorporation, immersion, and encapsulation [
To avoid incompatibility problems, due to the direct contact between conventional construction materials and PCMs, encapsulation method arises. Encapsulation eases the process of handling and incorporating of PCM into building materials, the leakage problem can be avoided, and the function of the construction structure can be less affected.
Macroencapsulation for PCM can present many different shapes, tubes, spheres, or panels, and can be obtained from several materials like aluminium or polymers. Macroencapsulated PCMs can be easily placed in ceilings [
The main goal of this section is to evaluate the feasibility of a new composite material, with inclusion of microencapsulated paraffin in cement based mortars, to be used in interior coatings for buildings. In order to be marketed within the European Union (EU) plastering mortars should respond to European Norm EN 998-1 [
Required tests for hardened mortars of general purpose (GP) and of lightweight (LW).
Test parameter | Test methods | Requirements | |
---|---|---|---|
GP | LW | ||
Dry bulk density |
EN 1015-10 | Declared range of values | Declared range of values: |
Compressive strength |
EN 1015-11 | CS I to CS IV | CS I to CS III |
Adhesion |
EN 1015-12 | ≥declared value and FP | |
Capillary water absorption | EN 1015-18 | W0 to W2 | |
Water vapour permeability coefficient ( |
EN 1015-19 a b | ≤declared value | |
Thermal conductivity |
Tabulated mean value | EN 1745:2002, Table A.12 |
The achieved mixture (used later on for further characterization) resulted from a set of preliminary analyses performed with the goal of evaluating the technical viability of the incorporation of microencapsulated PCM (industrially manufactured) into cement/lime based plastering mortar. Due to initial problems associated with the high cracking proneness of mortars containing PCM, the mixture composition was adjusted by an iterative process of trial and error, until the samples of the hardened mortar presented no visible cracking after the first hours of drying in controlled environment (with a temperature of
After a trial-and-error procedure that consisted in casting several test specimens (formulations A to L shown in Table
Mix proportions of formulations A to L and REFM and surface appearance of samples A to L.
Sample | Formulation |
Surface appearance | Comments | |
---|---|---|---|---|
A | Cement | 40.00 |
|
Appearance: fissuring/cracking without evident direction (aprox. |
PCM | 50.00 | |||
Sand (filler) | 10.00 | |||
|
||||
B | Cement | 40.00 |
|
Appearance: fissuring/cracking without evident direction (aprox. |
PCM | 50.00 | |||
Sand (filler) | 9.90 | |||
Cellulose ether | 0.10 | |||
|
||||
C | Cement | 25.00 |
|
Appearance: fissuring/cracking without evident direction (aprox. |
PCM | 50.00 | |||
Sand (filler) | 24.92 | |||
Cellulose ether | 0.08 | |||
|
||||
D | Cement | 25.00 |
|
Appearance: better appearance with less fissuring. |
PCM | 25.00 | |||
Sand (filler) | 49.92 | |||
Cellulose ether | 0.08 | |||
|
||||
E | Cement | 25.00 |
|
Appearance: better appearance with less fissuring. |
PCM | 25.00 | |||
Sand (filler) | 29.92 | |||
Industrial filler | 20.00 | |||
Cellulose ether | 0.08 | |||
|
||||
F | Cement | 25.00 |
|
Appearance: fissuring/cracking without evident direction (aprox. |
PCM | 25.00 | |||
Industrial filler | 49.87 | |||
Cellulose ether | 0.05 | |||
Calcium stearate | 0.08 | |||
|
||||
G | Cement | 25.00 |
|
Appearance: fissuring/cracking without evident direction. |
PCM | 25.00 | |||
Industrial filler | 49.85 | |||
Cellulose ether | 0.05 | |||
Calcium stearate | 0.08 | |||
Resins (VAE) | 0.02 | |||
|
||||
H | Cement | 10.00 |
|
Appearance: better appearance with less fissuring. |
Lime | 20.00 | |||
PCM | 25.00 | |||
Industrial filler | 42.80 | |||
Resins (VAE) | 2.00 | |||
Fibres (PAN) | 0.20 | |||
|
||||
I | Cement | 10.00 |
|
Appearance: better performance concerning cracking. |
Lime | 20.00 | |||
PCM | 25.00 | |||
Industrial filler | 42.70 | |||
Resins (VAE) | 2.00 | |||
Fibres (PAN) | 0.20 | |||
Aluminium powder | 0.10 | |||
|
||||
J | Cement | 10.00 |
|
Appearance: adequate behavior |
Lime | 10.00 | |||
PCM | 25.00 | |||
Industrial filler | 52.80 | |||
Resins (VAE) | 2.00 | |||
Fibres (PAN) | 0.20 | |||
|
||||
K | Cement | 10.00 |
|
Appearance: adequate behavior |
Lime | 10.00 | |||
PCM | 25.00 | |||
Industrial filler | 52.65 | |||
Resins (VAE) | 2.00 | |||
Fibres (PAN) | 0.20 | |||
Aluminium powder | 0.10 | |||
Cellulose ether | 0.05 | |||
|
||||
L | Cement | 10.00 |
|
Appearance: adequate behavior |
Lime | 5.00 | |||
PCM | 25.00 | |||
Industrial filler | 57.65 | |||
Resins (VAE) | 2.00 | |||
Fibres (PAN) | 0.20 | |||
Aluminium powder | 0.10 | |||
Cellulose ether | 0.05 | |||
|
||||
REFM | Cement | 12.00 | — | Table |
Lime | 2.48 | |||
Sand | 65.00 | |||
Industrial filler | 20.00 | |||
Fibres (PAN) | 0.05 | |||
Aluminium powder | 0.09 | |||
Cellulose ether | 0.09 | |||
Calcium stearate | 0.29 |
EN 998-1 [
The characterization of the developed plastering mortar had two main goals: the compliance with normative required values and consequent classification of the PCM mortar and the identification of the thermal complementary properties given by the presence of the PCM (like enthalpy and specific heat). The hardened mortars of the selected formulation L, now renamed as PCMM (PCM mortar), were submitted to a set of characterization tests required by European Norm EN 998-1 [
Results of the test performed to the composite mortar with formulation L (PCMM) and comparison to reference mortars (REFM).
Test parameter | Results | Classification of PCMM/comments | |
---|---|---|---|
PCMM (LW) | REFM (GP) | ||
Dry bulk density |
1170 | 1400 | LW/declared range of values: |
Compressive strength |
2.40 | 2.25 | CS I/similar behaviour. |
Adhesion |
0.35 FP: B | 0.30 FP: B | Similar behaviour. |
Capillary water absorption (intended use in external elements) | 4.89 | ≤4.0 | W0/similar behaviour. |
Water vapour permeability coefficient ( |
5–10 | <15 | EN 1745 [ |
Thermal conductivity |
0.29 | 0.61 | Similar behaviour when compared to LW mortars. |
Latent heat |
|
— | — |
Melting temperature |
|
— | — |
Melting temperature range |
23–25 | — | — |
Specific heat (solid) |
1.0 | 1.0 | EN 1745 [ |
A heat flow meter apparatus was used to determine thermal conductivity of the new composite material according to ISO8301:1991 [
The comparison of characteristics between PCMM and REFM is presented in Table
Traditionally EnergyPlus uses conduction transfer functions (CTF) to simulate surface constructions. These are linear equations, relatively simple, which allow the calculation of the conduction heat transfer through a completed layered building surface. However, with this method, it is impossible to include temperature dependent thermal properties, and thus modelling behaviours such as phase change enthalpy become unmanageable [
The inclusion of a new solution algorithm that utilizes an implicit finite difference procedure (CondFD) upgraded EnergyPlus to simulate the effect of PCM. This new model was tested and validated against multiple test suites [
This equation is complemented by (
The algorithm also permits including a temperature dependent thermal conductivity:
In this research the effect of introducing PCM in a plastering mortar on the external walls of a simple office cell located in Portugal is explored. A sensitivity analysis was performed, which included the study of the influence of material properties variation, such as melting temperature ranges and enthalpy, and the study of the influence of installing the office cell in different climatic regions. Discomfort due to overheating and cooling energy demand were the outputs used in the analysis.
The geometry adopted was an office cell like the one of ASHRAE Standard 140—Bestest Case 900 [
Material properties.
Element ID | Conductivity |
Density |
Specific heat |
Thickness |
---|---|---|---|---|
(a) Render | 1.00 | 1800 | 1000 | 0.005 |
(b) Insulation | 0.04 | 10 | 1400 | 0.04 |
(c) Block | 0.51 | 1400 | 1000 | 0.10 |
(d) Mortar | 0.30 | 1400 | 1000 | 0.03 |
Wall configuration.
Simulations were performed in two cities of Portugal, Lisbon and Porto, which represent different climatic regions. Both cities are located near the coast but, especially during summer, Lisbon is warmer than Porto. Figure
Monthly mean temperature.
All the simulations were performed with software EnergyPlus, for the cooling season, between 01/04 and 30/09, on an hourly basis and considering 60 time steps per hour.
The first performed analysis was the evaluation of the discomfort due to overheating, assuming a “free-floating” scenario (without cooling system). The discomfort was assessed by computing the degree-hours. The degree-hours (
It performed a sensitivity analysis that aimed to understand if overheating minimization can be achieved by the increasing of enthalpy amount in the mortar or by changing the PCM melting temperature range. A numerical simulation was carried out, which included 13 cases resulting from the combination of different phase change ranges (melting temperatures from 23/25°C to 26/28°C) with varied enthalpy values of 25, 100, and 200 kJ/kg, as well as the reference case without PCM, as can be observed in Figure
“Free-floating” scenario.
Case ID |
|
|
|
---|---|---|---|
PCM23/25_25 | 25 | 23 | 25 |
PCM23/25_100 | 100 | 23 | 25 |
PCM23/25_200 | 200 | 23 | 25 |
PCM24/26_25 | 25 | 24 | 26 |
PCM24/26_100 | 100 | 24 | 26 |
PCM24/26_200 | 200 | 24 | 26 |
PCM25/27_25 | 25 | 25 | 27 |
PCM25/27_100 | 100 | 25 | 27 |
PCM25/27_200 | 200 | 25 | 27 |
PCM26/28_25 | 25 | 26 | 28 |
PCM26/28_100 | 100 | 26 | 28 |
PCM26/28_200 | 200 | 26 | 28 |
REFM | — | — | — |
Enthalpy versus temperature.
In the second analysis, the effect of introducing an HVAC system in the office cell was evaluated by computing the energy demand for cooling assuming a temperature set point of 25°C. For this sensitivity analysis only two melting temperature ranges were considered, resulting in 7 cases (Table
HVAC scenario.
Case ID |
|
|
|
---|---|---|---|
PCM23/25_25 | 25 | 23 | 25 |
PCM23/25_100 | 100 | 23 | 25 |
PCM23/25_200 | 200 | 23 | 25 |
PCM24/26_25 | 25 | 24 | 26 |
PCM24/26_100 | 100 | 24 | 26 |
PCM24/26_200 | 200 | 24 | 26 |
REFM | — | — | — |
The comfort sensation is guaranteed by temperature level and stabilization inside a building space [
The first approach of the sensitivity analysis was for the “free-floating” situation. Degree-hours for 25°C basis were used as the evaluation parameter to assess the discomfort due to overheating. As an example, Figure
Assessed interior temperatures for the office cell located in Lisbon: (a) enthalpy effect, (b) melting temperature effect.
Attending to the results shown in Figure
Regarding Figure
The “overheating improvement” was evaluated by a percentage resulting from the difference of degree-hours
Discomfort analysis due to overheating inside an office cell placed in (a) Lisbon and (b) Porto.
These results are in line with other authors [
A similar analysis can be made for the improvement in the cooling energy demand when using PCM in the office cell with an HVAC system. The “energy savings” are evaluated by a percentage resulting from the difference in the annual cooling energy demand between the use of REFM as plastering in the office cell and the use of different PCMM. Attending to the results, shown in Figure
Energy savings analysis of the inside of an office cell placed in (a) Lisbon and (b) Porto.
On the analysis of the effect of introducing an HVAC system, the PCM presence was observed lowering the cooling energy demand necessary to maintain the temperatures inside the office cell close to the comfort temperature, 25°C.
Both sensitivity analyses produced very encouraging results that sustain future works on this research in order to optimize the use of PCM, adapting enthalpy and melting temperature ranges to climatic conditions and building’s envelope.
The main conclusions of this study are as follows. PCM can be incorporated into mortars without compromising the properties that are desirable for their application as plastering materials. The potential of advanced simulation tools to evaluate and optimize the usage of PCM materials in the indoor temperature control, allowing for an improvement in the comfort conditions and/or in the cooling energy demand, was explored in this paper. A sensitivity analysis regarding the enthalpy and melting temperature effect was performed and the temperature stabilization potential of the plastering PCM has been demonstrated. It was found that changes in the enthalpy value can produce a higher impact than varying the melting temperature of the PCM. Considering a “free-floating” space, the inclusion of a plastering mortar containing PCM with an enthalpy of 200 kJ/kg and a fusion temperature range between 25 and 27°C can improve the comfort conditions by 12%. For the office with an HVAC system, the inclusion of a plastering mortar containing PCM with an enthalpy of 200 kJ/kg and a fusion temperature range between 24 and 26°C can improve the cooling energy demand by 15%.
The authors declare that there is no conflict of interests regarding the publication of this paper.