Research Overview

Research Background: What Problem Did This Study Address?

The building sector is one of the largest contributors to carbon emissions. In China, rural construction is undergoing rapid renewal under the Rural Revitalization Strategy, but many new rural houses still rely on carbon-intensive materials such as reinforced concrete, fired bricks, cement mortar, and steel. If this construction model continues, rural housing development may lock in high embodied carbon and high operational energy demand for decades.

This study addressed the question of whether natural and regenerative materials can be used in real rural construction while still meeting structural, thermal, comfort, and carbon-reduction requirements. Earth and straw are both locally available, low-carbon materials with potential advantages in thermal mass, moisture buffering, and carbon storage. However, their practical scalability is often questioned because many studies remain at the material or laboratory level rather than full-scale building implementation.

To respond to this gap, the research team developed and built a full-scale rural prototype house in Tianshui, Gansu Province, a cold climate region of China. The building used a hybrid “light steel–poured earth–straw” system, combining a light steel structural frame, straw insulation, bamboo reinforcement, and poured earth wall layers.

The study did not rely only on design assumptions. The team combined construction documentation, on-site environmental monitoring, heat-flux measurement, EnergyPlus simulation, and life-cycle assessment. UbiBot GS1-AL4G1RS hygrothermal sensors were used to collect real temperature and relative humidity data inside and outside the building. These measurements supported the evaluation of indoor environmental stability and helped calibrate the operational energy model used in the carbon assessment.

The Specific Role of UbiBot in the Study

In this study, UbiBot GS1-AL4G1RS   hygrothermal monitoring sensors were used to record the real indoor and outdoor temperature and relative humidity conditions of the rural prototype building. The paper does not claim that UbiBot independently proved the low-carbon performance of poured earth and straw construction. Instead, UbiBot provided the real environmental monitoring data used to evaluate hygrothermal performance and support calibrated simulation.

The prototype building was located in Tianshui City, Gansu Province, China. The region belongs to China’s cold climate zone and has large seasonal and daily temperature variations. The building envelope used a composite wall system combining poured earth, straw insulation, OSB board, bamboo mesh, gypsum board, timber studs, and moisture-control membranes.

Seven UbiBot hygrothermal monitoring instruments were deployed indoors across different orientations and functional zones of the building. An additional instrument was placed in the courtyard of a neighboring household to monitor outdoor climatic parameters. The outdoor unit was placed in a shaded location to avoid direct solar radiation, helping it record representative outdoor air conditions rather than sun-heated sensor readings.

The UbiBot devices measured temperature from −20 °C to 60 °C and relative humidity from 10% to 90% RH. Measurements were logged every 5 minutes. The devices also supported network connectivity, allowing automatic data upload and storage on an online platform.

The monitoring lasted eight months. During this period, the building was unoccupied, all doors and windows remained closed, and active heating, cooling, and ventilation systems were not used. This was important because the researchers wanted to evaluate the passive hygrothermal behavior of the poured earth and straw envelope without occupant behavior or HVAC operation interfering with the data.

The UbiBot data were used in three main ways.

First, the measurements were used to compare indoor and outdoor temperature and humidity fluctuations across seasons. The researchers selected typical seven-day periods in winter, spring, and summer to evaluate indoor thermal stability, humidity buffering, time lag, and decrement factor.

Second, UbiBot temperature data were used to support EnergyPlus model calibration. The simulated indoor temperature was compared with monitored temperature, and validation indicators such as NMBE and CVRMSE were checked against ASHRAE Guideline 14 criteria.

Third, the calibrated model was used to estimate operational energy demand and operational carbon emissions over a representative building lifetime. In this workflow, UbiBot data formed the empirical basis for making the simulation closer to real building behavior.

Therefore, UbiBot’s role was environmental monitoring and model-support data collection. It supplied the indoor and outdoor hygrothermal records needed to connect the real prototype building with building-performance evaluation and life-cycle carbon assessment.

Research Methods and Data Collection Approach

The study combined construction prototyping, on-site monitoring, energy simulation, and life-cycle assessment.

The building prototype was constructed in rural Tianshui, Gansu Province. The research team first screened local soil through sedimentation tests and selected a silty loam soil sample suitable for poured earth after modification. The poured earth mix was optimized with gravel, sand, cement, sodium hexametaphosphate dispersant, and hemp fiber. The final mix used cement for strength, NaHMP for workability, and 25 mm hemp fiber to reduce shrinkage and cracking.

The building envelope was designed as a light steel–poured earth–straw composite system. The wall included gypsum board, straw insulation, OSB board, a hydrophilic permeable membrane, timber studs, poured earth, bamboo mesh, and cement mortar plastering. The straw insulation layer was 140 mm thick, and the poured earth layer was also 140 mm thick. The wall achieved a U-value of 0.30 W/(m²·K).

For on-site monitoring, two types of instruments were used. Heat flux sensors were embedded in the east, south, west, and north walls, with sensors placed at different depths across the poured earth and straw layers. These sensors recorded wall heat flux every 5 seconds. UbiBot GS1-AL4G1RS  hygrothermal sensors measured indoor and outdoor temperature and relative humidity every 5 minutes.

The monitoring period lasted eight months under unoccupied conditions. Doors and windows remained closed, and active heating, cooling, and ventilation were excluded from the monitoring process. Typical seven-day periods in winter, spring, and summer were selected for detailed analysis.

The researchers then built an EnergyPlus model using the Ladybug plugin on Grasshopper. The model was calibrated using measured indoor temperature data. After validation, the model estimated heating, cooling, lighting, and domestic hot-water energy demand. These results were converted into operational carbon emissions using the local grid carbon emission factor.

For life-cycle assessment, the study calculated embodied carbon from material production, transport, and construction stages. It then compared the light steel–poured earth system with conventional brick–concrete rural construction and a timber–poured earth alternative.

Key Research Findings

The monitored data showed that the poured earth and straw building significantly stabilized indoor temperature. Outdoor temperatures fluctuated strongly across seasons, while indoor temperatures changed much more gently. Across typical monitoring periods, outdoor temperature fluctuations ranged from 14.7 °C to 19.6 °C, while indoor fluctuations remained between 1.7 °C and 4.4 °C.

In winter, the outdoor temperature dropped as low as −16 °C, while the indoor low was −2.1 °C, about 13.9 °C higher than outside. In summer, outdoor temperatures reached up to 34 °C, while indoor temperatures remained between 22 °C and 28 °C. This indicated strong passive thermal buffering from the straw–poured earth wall assembly.

The time-lag analysis showed that the wall delayed heat transfer from outdoors to indoors. Average time lag was 5.3 hours in winter, 4.3 hours in spring, and 4.0 hours in summer. The decrement factor generally remained low, and the wall reduced outdoor temperature fluctuations by more than 70% across the three seasons.

Humidity monitoring showed that the composite wall also moderated indoor relative humidity. Outdoor humidity fluctuated much more strongly than indoor humidity. During the spring rainy period, outdoor relative humidity rose sharply to 93%, while indoor humidity increased more gradually. The paper reports that indoor relative humidity stayed within the 40%–60% comfort range for 85% of the monitored period.

Heat-flux monitoring showed asymmetric heat transfer. During spring daytime conditions, outdoor-side wall heat flux reached 12.7 W/m², while the indoor side reached only 2.3 W/m². This indicated that the wall absorbed and released heat while reducing heat transfer to the indoor side.

For carbon performance, the light steel–poured earth–straw system reduced net embodied carbon emissions by 28% compared with conventional brick–concrete construction under equivalent thermal performance. The annual operational carbon emissions were about 50% lower than the brick–concrete reference model. If timber replaced light steel as the structural system, total carbon emissions could be reduced by 40%, and net carbon emissions by 86% compared with conventional construction.

What This Means for Low-Carbon Rural Building Applications

This study shows that low-carbon rural buildings need to be evaluated through both material carbon and operational performance. A material may have low embodied carbon, but it must also maintain acceptable indoor comfort and reduce energy demand during use.

For rural housing in cold regions, the study suggests that earth and straw can do more than reduce embodied carbon. Their thermal mass, insulation, and moisture-buffering behavior can help stabilize indoor conditions in buildings exposed to large day-night and seasonal climate variations.

For building design, the monitored UbiBot data helped demonstrate that passive envelope performance can be quantified in real buildings. Instead of relying only on laboratory material values, the study used field temperature and humidity records to evaluate how the full wall system performed after construction.

For building-performance simulation, the study shows why measured data are important. Calibrated simulation gives a more reliable basis for estimating heating, cooling, and operational carbon emissions than unvalidated assumptions.

For rural construction policy, the study indicates that regenerative materials such as poured earth, straw, bamboo, and timber may help reduce the carbon footprint of rural building renewal, provided that construction systems, moisture control, durability, and cost are carefully addressed.

Application Value of UbiBot Devices

UbiBot GS1-AL4G1RS  demonstrated practical value as hygrothermal monitoring tools in this low-carbon building study.

First, the devices provided real indoor and outdoor temperature and relative humidity records. These data documented the environmental conditions experienced by the prototype building across seasons.

Second, the devices supported multi-point indoor monitoring. By placing sensors across different orientations and functional zones, the researchers could observe how indoor conditions varied spatially within the building.

Third, UbiBot data supported passive envelope performance evaluation. The monitored temperature and humidity curves were used to assess thermal buffering, humidity regulation, time lag, and decrement factor.

Fourth, UbiBot data supported energy model calibration. The measured indoor temperature data were compared with EnergyPlus simulation results, allowing the researchers to validate the model before calculating operational energy and carbon emissions.

Fifth, the networked data upload function supported long-term monitoring. Since the study required eight months of field data, automatic online storage made the environmental dataset easier to manage and use in later analysis.

Overall, UbiBot’s value in this study was not standalone carbon assessment. Its value was providing reliable, time-stamped hygrothermal data that connected the real prototype building with simulation-based operational carbon analysis and life-cycle assessment.

Extended Application Scenarios

The monitoring approach used in this study can be extended to several related scenarios:

1. Low-carbon rural housing monitoring
   Used to assess indoor temperature and humidity stability in rural houses built with earth, straw, bamboo, timber, or other bio-based materials.
2. Poured earth wall performance testing
   Used to record real hygrothermal behavior of poured earth walls under seasonal climate conditions.
3. Straw insulation and bio-based envelope evaluation
   Used to monitor moisture and thermal performance in straw-insulated walls, roofs, or retrofit assemblies.
4. Building simulation calibration
   Used to provide measured data for EnergyPlus, DesignBuilder, IESVE, or other building-performance models.
5. Passive building design validation
   Used to evaluate whether envelope design can reduce indoor temperature swings without active HVAC operation.
6. Rural building life-cycle assessment
   Used to supply operational performance data for whole-life carbon evaluation.
7. Moisture-risk monitoring
   Used to track indoor and outdoor relative humidity conditions in earth- and bio-based buildings.
8. Climate-adaptive architecture research
   Used to study how passive envelopes respond to cold climates, large daily temperature differences, rainfall, and seasonal humidity changes.

FAQ

1. Which UbiBot product was used in the study?

The paper mentions UbiBot GS1-AL4G1RS  hygrothermal monitoring sensors.

2. What data did UbiBot collect?

The UbiBot devices collected temperature and relative humidity data indoors and outdoors.

3. Where were the UbiBot sensors deployed?

Seven hygrothermal sensors were deployed indoors across different orientations and functional zones of the prototype building. One additional unit was installed in a neighboring outdoor courtyard to monitor external climatic conditions.

4. What was the sampling frequency?

Temperature and relative humidity were recorded every 5 minutes.

5. How long did the monitoring last?

On-site monitoring lasted eight months. The paper selected typical seven-day periods in winter, spring, and summer for detailed analysis.

6. How were the UbiBot data used?

The data were used to evaluate indoor temperature and humidity stability, assess wall hygrothermal performance, and calibrate the EnergyPlus model used for operational carbon calculation.

7. Did UbiBot measure heat flux?

No. Heat flux was measured by separate LHYRLCH4-1 heat flux sensors at 5-second intervals. UbiBot monitored temperature and relative humidity.

8. Did UbiBot calculate carbon emissions?

No. Carbon emissions were calculated through life-cycle assessment and EnergyPlus-based operational energy simulation. UbiBot supplied measured environmental data that supported model calibration and performance analysis.

9. What was the main building-system result?

The light steel–poured earth–straw system improved indoor hygrothermal stability and reduced net embodied carbon emissions by 28% compared with conventional brick–concrete construction under equivalent thermal performance.

10. Why is this research important?

It provides full-scale evidence that poured earth and straw construction can reduce carbon emissions while improving indoor thermal and humidity stability in rural cold-climate housing.