What is Thermal Mass?

To uncerstand why Hempcrete is such a good insulator, it's helpful to look it up. I didn't understand what it was till I looked it up 2 months after learning about Hempcrete. 

Info from a Google search for Hemp Thermal Mass

Thermal mass hemp, also known as hempcrete, is a building material that stores heat energy and releases it slowly to regulate temperature. This property makes hempcrete an energy-efficient material that can reduce the need for heating and cooling. 

How it works

• Stores heat

  Hempcrete's thermal mass allows it to store heat energy within the material itself. 
• Releases heat

  When the surrounding temperature drops, hempcrete releases the stored heat. 
• Regulates temperature

  Hempcrete's thermal mass helps to regulate the temperature of a building, reducing the need for heating and cooling.

Benefits

• Energy efficient

  Hempcrete can reduce energy demands for heating and cooling. 
• Insulating

  Hempcrete is a good insulator, which can help keep heat inside in the winter and keep heat out in the summer. 

Carbon sink

Hempcrete can capture carbon dioxide (

$C{O}_2$

) from the air, which can help to reduce greenhouse gas emissions.

• Healthy indoor environment

  Hempcrete is vapor permeable and hygroscopic, which can create a healthy indoor environment. 

Materials 

• Hemp: The woody core of the hemp plant is used to create hempcrete.
• Lime-based binder: The binder is used to create the bio-composite material.

Generative AI is experimental.

Passive Solar Design - What is thermal mass?

What they don't tell you about Thermal Mass

https://www.sciencedirect.com/science/article/abs/pii/S0360132321007745

Building and Environment

Volume 206, December 2021, 108377

Hempcrete building performance in mild and cold climates: Integrated analysis of carbon footprint, energy, and indoor thermal and moisture buffering

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Highlights

• •
  Whole-building LCA and HAM simulation of hempcrete and conventional rainscreen buildings.
• •
  Difference in operational GWP is minimal compared to embodied GWP savings.
• •
  Solar heat gain is reduced for the hempcrete building.
• •
  Improved indoor temperature and humidity modulation and condensation resistance for the hempcrete building.
• •
  Inclusion of moisture and thermal buffering effects important for accurate results.

Abstract

The use of hempcrete as a bio-based alternative to conventional building materials was investigated through a building life cycle carbon footprint analysis of a conventional wood-frame enclosure and a hempcrete enclosure. Embodied emissions were determined using the Athena Impact Estimator. An in-house developed whole building hygrothermal model was validated using experimental data and then used to assess the operational energy including the dynamic interaction of thermal and moisture buffering with building heating and cooling loads.

The higher thermal mass of hempcrete was shown to increase heating energy consumption and reduce cooling energy consumption due to a reduction in solar heat gain. Therefore, for the mild and cold climates studied here, cooling energy savings were mostly overtaken by increased heating energy consumption. The difference in energy performance was minimal compared to the savings in embodied emissions for the building life cycle carbon footprint, which showed a 23.2% and 9.9% reduction in emissions for the hempcrete building with a 50-year lifespan.

Due to the high moisture capacity of hempcrete, ignoring the moisture-dependency of thermal conductivity can result in underestimation of energy consumption. Moisture buffering had little effect on energy performance, however, it can greatly reduce condensation risk, thereby improving IAQ and durability.

Introduction

According to the United Nations Environment and International Energy Agency [1], 39% of global CO2 emissions are due to the buildings and construction sectors. Of these emissions, 72% is attributed to the operational phase, where energy is used to heat, power, and cool the space. The other 28% are attributed to the embodied emissions of the construction and material manufacturing processes. To date, the greatest efforts have been directed towards reducing operational emissions, often by installing thicker insulation to increase the thermal insulation value of the building enclosure. As a result, though overall life cycle emissions have decreased, the embodied emissions have stayed at the same level or even increased. In new high-performance buildings such as passive houses and net-zero energy/emissions buildings (NZEB) the contribution of embodied emissions accounted for about 50% of total life cycle emissions and surpassed 90% in extreme cases [2]. When comparing the life cycle performance of European buildings to the Swiss SIA 2040 benchmark for building GHG emissions, most cases, including high-performance buildings, exceeded the target 11 kgCO2e/m2a [2]. These results suggest that new high-performance building standards, which mainly focused on reducing operational energy, were not sufficient for meeting GHG emission reduction targets. Thus, some of the focus has shifted to investigating bio-based natural materials which undergo less energy intensive manufacturing processes and contain low embodied emissions as a replacement for current building materials.

One such material is hempcrete (also known as hemp-lime or hemp-lime concrete). Hempcrete is a composite material created from a mix of hemp plant hurd (or hemp shiv), lime-based binder, and water. The global warming potential (GWP) of hempcrete varies due to differences in material composition, density, and system boundaries, but life cycle assessment studies consistently conclude hempcrete to be a net carbon negative building material sequestering up to −135 kgCO2e/m3 as a result of carbon sequestered during the growth phase and lime binder carbonation [[3], [4], [5], [6], [7]].

Hempcrete is a lightweight insulating material with a thermal conductivity generally ranging from 0.05 to 0.138 W/(m·K) depending on density [8]. Though the thermal conductivity of hempcrete is higher than most conventional insulation products, the material is generally installed as infill material to create monolithic walls, ensuring a thickness that provides similar R-values to conventional wall assemblies. This application creates enclosures with high thermal mass. Its heat capacity ranges from 1000 to 1700 J/(kg·K) when dry [8], to over 2900 J/(kg·K) at 99% relative humidity (RH) [9]. The effect of thermal mass presents itself in dynamic conditions by allowing the material to store heat energy within itself and release the heat when the surrounding temperature is lower, thereby dampening temperature variations. This effect is ignored in simple steady-state thermal calculations, however there is evidence that thermal mass may have a significant effect on the energy performance of a building. Specifically, high thermal mass is effective for reducing cooling loads in hot climates [10,11]. Conversely, Reilly and Kinnane [11] also highlight the increased heating loads corresponding with high thermal mass for intermittently heated spaces in cold climates. As such, the thermal performance of hempcrete needs to be characterized not only with the R-value normally used to specify building envelope components in building codes but also in consideration of the thermal mass effect and climate zone through dynamic simulations.

Porous building materials such as hempcrete exhibit the ability to dampen variations in indoor humidity by absorbing and desorbing moisture in the air. This phenomenon is called moisture buffering and is generally quantified by a material's moisture buffer value (MBV). Hempcrete has a MBV ranging from 1.99 to 2.15 kg/(m2·%RH) [12]. The inclusion of moisture buffering effects has been shown to have a great influence on the indoor humidity [[13], [14], [15]]. Furthermore, Tran Le et al.'s [16] examination of the transient performance of a hempcrete building for one month in January shows that due to hempcrete's capacity to hold moisture, the thermal conductivity of the material is increased and assuming constant thermal conductivity resulted in a 5.4% underestimation of heating energy in Nancy, France. Thus, the dynamic simulations must also be able to take into account the moisture content within the material as well as the moisture exchange between the air and the material when simulating the performance of hempcrete.

Though the insulation value of a hempcrete enclosure can be the same as that of a conventional enclosure, there are dynamic thermal and moisture effects which may affect the energy performance of a hempcrete enclosure. As such, it is unclear if the gains from the reduced embodied emissions of a hempcrete enclosure would be overtaken by the difference in operational emissions compared to conventional enclosures.

In order to assess the dynamic effects of thermal mass and moisture buffering on the energy performance of hempcrete, a modelling tool capable of simulating indoor moisture buffering as well as building heating and cooling loads is needed. As such, whole-building hygrothermal models such as HAMFitPlus [17] are the ideal tools to encompass the interactions between the indoor environment, the building enclosure, the outdoor environment, and the mechanical system [18]. In general, there is a lack of comprehensive studies that focus on whole-building hygrothermal performance of hempcrete buildings as most studies are material-level and wall-level. Some studies which have examined the whole building performance of hempcrete are focused on model validation and do not include LCAs [16,19,20]. The study by Maalouf et al. [21] compares hempcrete with recycled-PET facades and includes a detailed carbon footprint comparison, however, the factors impacting differences in operational energy are less explored. Similarly, Florentin et al. [22] studied the life cycle energy and carbon performance of hempcrete compared to aerated autoclaved concrete, however, the operational energy demand was assumed to be the same for both materials.

For further development and use of hempcrete buildings in cold and mild climates it is important to have insight on whether the gains from the reduced embodied emissions of a hempcrete enclosure would be overtaken by increases in operational emissions; the effects of moisture and thermal mass on the energy performance of a hempcrete building given its hygrothermal active behaviour; and the moisture buffering potential for buildings with different indoor moisture loads and ventilation. The aim of this paper is to assess the whole-building performance of hempcrete buildings from the perspective of life cycle carbon emissions, energy use, and their ability to modulate indoor air temperature and humidity.

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Section snippets

Methodology

Currently, hempcrete is most often used to construct wood-frame residential houses due to its non-load bearing nature and its compatibility with wood. The carbon footprint as well as the thermal and moisture performance of a residential hempcrete building (Building H) are assessed in comparison with a typical conventional split-insulated wood-frame building (Building C). Apart from the composition of the exterior wall enclosure of the same R-value, the two buildings are identical and are

Experimental setup

HAMFitPlus is validated using field experimental measurements conducted in test buildings [23]. The monitored buildings are the Whole-Building Performance Research Laboratory (WBPRL), which is a set of two identical test buildings located at the south end of the BCIT campus located in Burnaby, Canada. Each building consists of an EPS-insulated concrete foundation and HSS beam and column structure covering 17.84 m2 floor area and 3.0 m interior height [24]. Fig. 1 presents the floor plan of the

Study buildings (Building C and Building H)

The floor plans for Building C and Building H are shown in Fig. 3, which are identical except for the wall enclosure compositions. Hempcrete is most commonly applied to residential construction; therefore, a two-bedroom residential dwelling occupied by a family of three (two adults and one child) is considered for the study. The floor plans are used to calculate the partition wall area which may absorb and desorb moisture and affect indoor humidity as well as to account for the space thermal

Life cycle carbon footprint

The total life cycle carbon footprint of the two buildings are determined through the summation of embodied and operational GWP for a building lifespan of 50 years. The Athena Impact Estimator [38] is used to determine the embodied emissions and the associated GWP of the buildings. Athena provides detailed cradle-to-grave LCA results based on ISO 14040/14044 compliant data and organized by modules A, B, C, and D which categorize the life cycle emissions into product, construction process, use, 

Conclusion

The performance of hempcrete as a building material in mild and cold climates is examined through comparison of a conventional wood-frame enclosure (Building C) and a hempcrete enclosure (Building H) in Vancouver and Toronto. The whole-building hygrothermal model, HAMFitPlus, is first validated using experimental data before being used to study the effect of thermal mass and moisture on the hempcrete building energy performance and indoor air temperature and RH.

In the climates studied, the

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors are grateful for the financial support provided by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chair (CRC/DG) and the School of Construction and the Environment at the British Columbia Institute of Technology (138121).

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