Active Insulation System Research Articles

Development and performance evaluation of active insulation systems using solid-state thermal switches

Traditional building envelopes have passive insulation systems that cannot respond to dynamic changes in the environment. An Active Insulation System (AIS) consists of Active Insulation Materials (AIMs) that dynamically vary the thermal conductivity of the insulation system. Several researchers have evaluated the impact of AIS on building thermal and energy performance by using simulation tools. Up to 70% savings in annual heating and cooling energy and significant reductions in peak demand have been predicted for some climates with wall systems employing AIS. However, materials and assembly development still need a cost-effective product that achieves the required performance. In this study, we present the process of developing an AIS that we will install in a test hut for its performance evaluation. Minimum performance criteria of the AIS system are developed based on R-low/R-high ratio, required time and efficiency to switch states, and cost estimates. The following steps during this study are creating the concept to meet the requirements, predicting the performance via simulations, developing the experimental setup for bench-scale testing, and finally, constructing a full-scale wall assembly and monitoring the performance when exposed to environmental chamber tests. The selected approach uses off-the-shelf products to create an AIS that can switch R-value between 0.98 ft2·°F·h/BTU (0.173 m2·K/W) and 5.81 ft2·°F·h/BTU (1.02 m2·K/W) and have a switching time of less than one minute between R-high and R-low.

Performance assessment of active insulation systems in residential buildings for energy savings and peak demand reduction

Active insulation systems (AISs) in buildings are envelopes that integrate thermal insulation, thermal energy storage, and controls. Although different designs for AISs have been proposed in the literature, a comprehensive analysis of feasible AISs is lacking. This paper discusses the energy performance, peak demand reduction potential, and performance characteristics of an AIS that uses a concrete wall as thermal mass sandwiched between two solid-state thermal switches (STSs). These STSs change their thermal conductivity using an on/off metal switch to create or break a thermal bridge across the STS. This paper first describes the experimental setup, used to determine the ratio of thermal resistance during R-high (low thermal conductivity) and R-low (high thermal conductivity) states of the STSs. This ratio was then used in whole-building energy simulations to evaluate the performance of AIS walls across different climate zones with/without a freeze timer of 60 min. The timer was added to reduce the number of switches of STSs from one state to another, and hence the energy needed for these switches. Analysis of the switching frequency and interval of STSs, thermal conductivity of walls, impact of wall orientation, and heat transfer through the wall from the use of AIS at different climate zones/locations were performed. The simulation results show that the AIS can achieve energy savings ranging from ∼ 980 to 2,290 kWh in a single-family home with a floor area of ∼ 220 m2 compared with an IECC 2018 baseline. The energy savings was higher in dry climate zones which represent 17% of residential buildings in the United States, compared to humid or marine climate.

Tradeoffs in optimization of Active Insulation Systems and HVAC: A case study in residential buildings

Active insulation systems (AIS) have been conceptualized to make buildings more responsive to changing environmental conditions, creating energy efficiency and flexibility gains. Building flexibility and efficiency can be further improved if the building is also equipped with optimized HVAC system controls. Optimal control of AIS and HVAC systems can be used to activate thermal mass, and past work has quantified the potential benefits of jointly optimizing both systems. In this work, we more fully elucidate and evaluate the potential tradeoffs between optimal control of these technologies with respect to building energy use and peak demand–including different configurations of heat pump systems and integrated building thermal energy storage. Tradeoffs are revealed by applying a multi-objective optimal control framework and comparing the Pareto optimal sets across various system configurations. Discussion of the results provides insights into how buildings can be best designed and controlled to achieve both energy efficiency and flexibility.

Revisiting heat losses in lab-scale distillation columns: Quantification, improvement, and influence on miniaturized 3D-printed packings

Lab-scale distillation columns with a diameter of 50 mm (DN50) are widely established for experimental investigations during process development and scale-up. In recent years, the diameter was successfully reduced to 20 mm (DN20) by utilizing additive manufacturing to attain new miniaturized packings that attend to the specific miniaturization obstacles. However, since heat losses have a higher influence in a DN20 column, this publication investigates their impact on the operation and data obtained from an additively-manufactured laboratory distillation column. A comparison is provided between the state-of-the-art DN50 size and a miniaturized DN20 size. The heat loss rate is estimated by simulations and experimentally measured for both column diameters with and without thermal insulation. The impact on the internal flow variation and the gas load (F-factor) uncertainty is presented. The findings provided motives for further improvement to minimize the heat loss rate in the DN20 column. This led to the development of a novel active insulation system where custom-dimensioned flexible silicon heaters are utilized for external heat compensation. The system reduces the heat losses significantly and led to a decrease in the F-factor uncertainty from ± 0.09 Pa0.5 to 0.04 Pa0.5 compared to the passively insulated case. Finally, the effect of the heat loss reduction on the mass transfer efficiency is discussed using two additively-manufactured packings, a 3D-printable version of the Rombopak 9M structure (RP9M-3D) and a new miniaturized packing (XW-Pak). The RP9M-3D showed a decrease in separation performance with heat loss reduction while the performance of the XW-Pak remained unaffected.

Evaluating optimal control of active insulation and HVAC systems in residential buildings

Recently, active insulation systems (AIS) have been conceptualized in building envelopes to optimally modulate thermal resistance in response to changing environmental conditions. Building flexibility can further be improved if the building is also equipped with optimized heating, ventilating, and air conditioning (HVAC) control. In this work, we investigate the annual potential benefits of jointly optimizing AIS and HVAC system controls in both heating and cooling days over all climate zones (CZs) in the U.S. To reduce the computational complexity of applying model predictive control (MPC) to annual operations and detailed whole-building energy models, timeseries clustering was used to identify a set of representative days for optimizing in each climate zone. To isolate the increase in benefits from this joint optimization, we compare the performance to cases where the AIS and HVAC controls are optimized separately. Results indicate savings potential in all CZs, with the largest annual average savings of 9.02% and 4.02% observed in the cooling days with large daily temperature swings and heating days with cold sunny conditions, respectively. Savings patterns across climate zone, day types, and HVAC modes (i.e., heating or cooling) are also discussed along with the implications of important system design variables.

Modeling and demand-based control of responsive building envelope with integrated thermal mass and active thermal insulations

The static nature of current envelope design and operation is diametric to the mutable and transient forces and energies acting on our building stocks. Responsive building envelopes (or RBEs) have shown substantial energy saving potential for buildings by adaptively providing passive cooling/heating. In this research, an easy-to-implement yet flexible ‘demand-based’ control rule is proposed based on demand analysis to optimally control RBEs that integrate active insulation systems (AISs) and a sensible thermal energy storage (TES) layer. The controller developed herein calculates the desired thermal resistance for AIS layers and provides on-demand control of the heat flow into and out of the thermal mass to reduce AC load. It provides several benefits over the simple temperature-based controllers while does not require the complex formulation as needed for model predictive control. To quantify the thermal behavior and energy performance, a thermal network model is developed for RBEs to perform wholebuilding energy simulations of a residential thermal zone in six representative cities in the US. The results show apparent benefits of demand-based control strategy over traditional temperature-based control by offering higher energy savings and LPD reduction, especially in mild climate zones and during transitional seasons. Some design and implementation considerations for REBs with integrated AISs and TES are also discussed.

Peak cooling load shift capability of a thermal energy storage system integrated with an active insulation system in US climate zones

This study aims to evaluate a thermal energy storage (TES) system integrated with an active insulation system (AIS) to form a TES + AIS integrated wall system as a partition and as a secondary cooling system to shift the peak load and reduce cooling energy consumption. To understand and demonstrate its cooling performance, the TES + AIS integrated wall system was installed in an office building in Oak Ridge, Tennessee. To investigate the effect of the TES + AIS integrated wall system in a typical office building and various climate zones, the US Department of Energy’s prototype office building model was modified to accommodate the proposed system. Results showed that the minimum size of the proposed system to achieve energy savings varies depending on climate conditions. The minimum size of the proposed system for cooling energy saving and shifting peak cooling demand in climate zones 2, 3, and 5 is 29.7 m2, whereas it is 44.6 m2 in zones 4 and 6. By installing the minimum size of the proposed system, 11.3 % to 16.4 % of cooling energy can be shifted during discharge hours in a representative summer day.

Empower Wall: Active insulation system leveraging additive manufacturing and model predictive control

Buildings are one of the largest energy consumers worldwide, using large amounts of energy during their construction and for climate control during operation. Active insulation systems (AIS) have been shown to reduce the energy needed for climate control in buildings by dynamically regulating the heat transferred between a building’s interior and exterior. Infrastructure-scale additive manufacturing (AM) has the potential to reduce the resources needed for building construction. Combining these two technologies into a single building envelope would create a path towards more sustainable buildings. A test was conducted for the Federal Energy Management Program (FEMP) Energy Exchange training and trade show, in August 2021, to investigate a new building envelope design, termed the Empower Wall, that utilized an AIS and was constructed using AM. Model predictive control was implemented to manage operation of the Empower Wall in concert with the existing HVAC system. The prototype system demonstrated that the Empower Wall lowered total energy consumption and reduced the cost of energy used.

Model predictive control for active insulation in building envelopes

Active insulation systems (AISs) refer to building envelopes with insulation materials that can change their thermal conductivity and are coupled with thermal mass to reduce building energy consumption and peak power. In this research, a novel optimal control approach is proposed to evaluate the maximum theoretical energy and cost-saving potential of AISs. A time-varying model predictive control (TV-MPC) controller was used to optimally select the AIS mode and simultaneously determine the operation of the heating, ventilation and air conditioning (HVAC) system so that the maximum saving potential of the entire system can be realized. To comprehensively evaluate the power shifting flexibility of AISs, two optimization objectives—minimizing weekly electric energy consumption and minimizing weekly electricity cost—were considered. The summer season simulation results show that under the first objective, more than 50% electric and thermal energy was saved when the upper boundary of the indoor air temperature was set to 25 °C. Under the second optimization objective, 38% of the cost was saved. It can be expected that the developed approach can be easily applied to multiple types of AISs with different mechanisms.

Performance evaluation of a dynamic wall integrated with active insulation and thermal energy storage systems

Thermal energy storage systems in buildings can store cooling/heating energy during non-peak load hours or when renewable energy sources are available for later use when demanded. Using the building envelope as a thermal battery can help to shave the peak load, reduce the burden in electric grids, and enhance the occupant's thermal comfort. Sensible energy storage on wall systems such as thermally activated building systems can provide an active thermal storage strategy. However, most of the stored energy is used through passive means directed by the thermal lag, which can impede the on-demand release of the stored energy. Integrating active insulation systems with building thermal storage systems can increase the flexibility of charging and discharging time and duration. In this study, a wall system equipped with an active insulation system and thermally activated storage system was designed, and its performance on active cooling energy contribution was studied. The performances of energy storage (charging), release (discharging) of the thermal energy storage energy, and the active insulation system were studied separately and together as an integrated system. Results showed that the thermal properties of the thermal energy storage core material and the pipe spacing of both embedded pipes in the thermal energy storage and hydronic pipes used in the active insulation system affected the wall performance the most out of all the tested wall system parameters. During discharging, the heat flux into the wall was as high as 81.92 W/m2. The active insulation system's dynamic R-value varied between less than 1ft2•°F•h/BTU (0.18 m2•K/W) to 98% of the equally thick foam insulation's R-value.

Interior thermal insulation systems based on wood fiberboards: experimental analysis and computational assessment of hygrothermal and energy performance in the Central European climate

Two interior thermal insulation systems based on wood fiberboards are analyzed. The first system is composed of soft and hard fiberboards, the second one utilizes a capillary active fiberboard with incorporated water vapor retarder. The hygrothermal and energy performance of the systems in the climatic conditions of Central Europe is assessed using a combination of experimental and computational methods. A laboratory critical experiment is performed at first. The measured temperature and moisture profiles are then used for the validation of computational model of coupled heat and moisture transport, which is applied for hygrothermal and energy simulations. After the successful validation procedure, the model is used for the annual assessments. The energy assessment of the two-layer system shows excellent results from the point of view of energy savings (79 % improvement) but its hygrothermal assessment reveals possible shortages related to excessive hygric straining of the wall on the exterior side. The capillary active insulation system with water vapor retarder, which is able to keep moisture in the envelope within the hygroscopic range, exhibits only slightly worse energy performance (66 % improvement) but much better hygric performance than the two-layer system.

Active thermal insulation as an element limiting heat loss through external walls

The authors present the preliminary results and analyses of research performed in an experimental residential building located in the town of Nyiregyhaza in Hungary. The building is equipped with an innovative system for direct coupling a ground heat exchanger with a wall heat exchanger. In 2012, the creator of the system, Tamas Barkanyi, obtained patent for active thermal insulation of buildings. In this paper, the authors attempt to answer the question of to what extent the active insulation system can replace the commonly used standard passive insulation systems. The initial results of the research lead to the conclusion that active thermal insulation significantly improves the insulation parameters of the external wall. In the analyzed periods, the reduction of the total amount of heat loss through external walls was from 53% in February to 81% in November. The equivalent thermal transmittance Ueq of the analysed wall was dependent upon local climate conditions and amounted to 0.047 W/(m2K) in November and 0.11 W/(m2K) in March, while the standard transmittance value was 0.282 W/(m2K).The obtained positive research results should be the basis for the implementation of an innovative system in NZEB buildings.

Effect of façade impregnation on feasibility of capillary active thermal internal insulation for a historic dormitory – A hygrothermal simulation study

Internal insulation of external walls is known to create moisture performance challenges due to increased moisture levels and condensation risk on the cold side of the insulation. Capillary active/hydrophilic insulations have been introduced to solve these moisture problems, since they are able to transport liquid moisture to the inner surface and enable it to dry. Experience with this insulation type is rare in Denmark. In hygrothermal 1D computer simulations, several more or less capillary active insulation systems (AAC, calcium silicate, IQ-Therm) in various thicknesses (30–150mm) have been tested for their hygrothermal performance. The original construction was a 228mm solid brick masonry wall in a Copenhagen historic dormitory. All simulated systems showed critical relative humidity values above 80% and high risk of mould growth behind the insulation and some also on the interior surface. A moisture safe construction was only achieved when exterior façade impregnation shielding against driving rain was added. The best system showed acceptable relative humidity values both behind the insulation and on the interior surface, a significant increase in minimum temperature on the interior surface, and a reduction of heat loss through the external wall by 85%. The solely application of impregnation also resulted in a moisture safe solution with significant improvements in all parameters and heat loss reduction by 45%. The main conclusion is that capillary active insulation may not be feasible on solid bare masonry walls without additional driving rain protecting especially in case of multi-storey buildings with thin walls in high precipitation areas.

Capillary Active Interior Insulation Systems for Wall Retrofitting: A More Nuanced Story

ABSTRACTTo thermally upgrade exterior masonry walls, interior insulation is often the only possible retrofitting technique, especially when dealing with historic buildings. Unfortunately, it is also the riskiest post-insulation technique, as frost damage, interstitial condensation, and other damage patterns might be induced. To diminish those risks, nowadays so-called capillary active interior insulation systems are often promoted. These systems aim a minimal reduction of the inward drying potential, while interstitial condensation is buffered.Currently, several capillary active systems are on sale. These different types have, however, widely varying properties. In this article, a closer look at the hygrothermal properties and the working principle of a number of “capillary active” interior insulation systems is made. The spread in capillary absorption coefficients and the vapor diffusion resistances of the different systems is discussed and their influence is illustrated. Based on all this, a more nuanced view on capillary active insulation systems is pursued.Abbreviations: AC: aerated concrete; CaSi: calcium silicate; GM: glue mortar; GB: gypsum board; HAMFEM: Heat Air and Moisture Finite Element Method; MW: mineral wool; PE: polyethylene; PIR: polyisocyanurate; PUR: polyurethane; VIP: vacuum insulation panel; WFB: wood fiber board; XPS: extruded polystyrene; sddry: dry vapor diffusion resistance factor; µdry: dry vapor diffusion resistance

Interior insulation for wall retrofitting – A probabilistic analysis of energy savings and hygrothermal risks

Interior insulation is often the only possible post-insulation technique to improve the thermal performance of single leaf masonry walls. As a result of potential damage patterns such as frost damage, interstitial condensation and mould growth however, there is often some reluctance to adopt this technique. To fully exploit the capacity for energy savings offered by interior insulation while avoiding hygrothermal failure, a reliable risk assessment is extremely important. This requires a probabilistic approach, since the uncertainty of all influencing parameters might result in widely varying results.As, so far, no real methodology is available to select the interior insulation system and thickness resulting in the best balance between energy savings and hygrothermal risks, this paper presents a decision tool based on a Monte Carlo analysis. Additionally, the influence of the rain load and some masonry characteristics is discussed. In the study, both vapour tight interior insulation systems and a capillary active insulation system are considered. Overall, vapour tight systems tend to be preferable for structures that are resistant to frost damage. For buildings sensitive to frost damage or when wooden beam ends are present, however, capillary active systems are shifted forward.

Capillary active interior insulation: do the advantages really offset potential disadvantages?

Nowadays, capillary active interior insulation systems are often promoted because of their ability to avoid interstitial condensation, while a drying out remains possible. Additionally, their alleged performance to regulate the indoor climate is often used as a selling point. This paper compares the hygrothermal performance of a capillary active interior insulation system to this of a traditional vapour tight system. Where the previous studies on capillary active insulation systems mainly focused on historical buildings, this study investigates the applicability to standard single leaf masonry walls. Apart from the risk on interstitial condensation, also the impact on the indoor climate and the impact that wind-driven rain has on the hygrothermal behaviour of the retrofitted wall have been analysed. The capillary active system is found to be more sensitive to small modifications of the wall structure (e.g. interior finishing coat, wall thickness), while hardly any differences could be observed for the wall with a vapour tight system. In addition, wind-driven rain can hamper a good hygrothermal behaviour of a capillary active interior insulation system by inducing a lower thermal resistance or an increased indoor relative humidity. Therefore, it should be checked if the advantages of using capillary systems offset the potential disadvantages. A case-specific study is recommended to ensure the applicability of a capillary active interior insulation system.

A comparison of the hygric performance of interior insulation systems: A hot box–cold box experiment

Abstract To increase the thermal performance of massive masonry walls, exterior or interior insulation can be used. The latter insulation technique is the most risky, though forms for example in cases of historical buildings, buildings with a worth-preserving facade or buildings in the urban context the only solution to increase the thermal performance of the wall. The current article compares the hygric performance of massive masonry walls provided with different interior insulation systems. To do so, small test walls are placed all together in a single hot box–cold box. The total moisture increase in the walls is measured by weighing the test walls. In addition, to investigate the working principle of the insulation systems the moisture distribution across the wall assemblies is investigated using the X-ray projection method. In the analysis capillary active as well as more standard non-capillary active insulation systems are investigated. For the imposed quasi steady-state winter condition, the increase of stored moisture inside walls with a capillary active system is found to be higher than for walls with a traditional vapour tight system.

An Innovative Use of Renewable Ground Heat for Insulation in Low Exergy Building Systems

Ground heat is a renewable resource that is readily available for buildings in cool climates, but its relatively low temperature requires the use of a heat pump to extract it for heating. We developed a system that uses low temperature ground heat directly in a building wall to reduce transmission heat losses. The Active Low Exergy Geothermal Insulation Systems (ALEGIS) minimizes exergy demand and maximizes the use of renewable geothermal heat from the ground. A fluid is pumped into a small pipe network in an external layer of a wall construction that is linked to a ground heat source. This decouples the building from the outside temperature, therefore eliminating large peak demands and reducing the primary energy demand. Our steady-state analysis shows that at a design temperature of −10 °C the 6 cm thick active insulation system has equivalent performance to 11 cm of passive insulation. Our comparison of heating performance of a building with our active insulation system versus a building with static insulation of the same thickness shows a 15% reduction in annual electricity demand, and thus exergy input. We present an overview of the operation and analysis of our low exergy concept and its modeled performance.

736 床衝撃音のアクティブ遮音パネルシステム : 簡易モデルにおける音響放射パワーの解析

736 床衝撃音のアクティブ遮音パネルシステム : 簡易モデルにおける音響放射パワーの解析

Analysis of an active high-temperature thermal insulation system

An active thermal insulation system consisting of a semitransparent porous medium with gas injection is considered for protecting a structure from intense radiation flux (≈5 MWm −2). The dependence of the thermophysical properties on temperature and dissociation are taken into account. Air, hydrogen, and dissociating ammonia are considered as representative gases. The effects of dissociating and nondissociating gases on temperature distributions in the gas and solid are examined. The active insulation system reduces the thermal penetration depth as little as a few millimeters in thickness. The present protection system is most effective when the advection-radiation parameter N c / N R is larger than 1 or 2.