Zero Emission Temporary Habitation: A Passive Container House Acclimatized by Geothermal Water

ZEBRA means “zero energy consumption building totally renewable addicted.” It is a new building concept with low energy consumption from fossil fuels. It has been designed to preserve the comfort conditions during both summer and winter, and to minimize primary energy needs. A patent by Dumas [1] has inspired the LESP (low exergy structured panel) adiabatic panel [2], which is the main component of ZEBRA.

With the revitalization of the economic crisis the studies, which have started during 1970s and 1980s and then abandoned because of the illusion of energy supply at low cost, have become the pillars of new projects.

Wellness conditions, thermophysical properties and thermal quality of the envelope of the buildings are the major issues for the future.

Several techniques have been developed to increase energy efficiency and comfort conditions [3–5]:

1. (1)

   prefabricated cladding for thermal insulation

2. (2)

   vented facades

3. (3)

   thermal insulations by high-tech materials

The following applications are also of common utilization:

1. (1)

   Trombe wall for capturing solar radiation

2. (2)

   Radiant floor or ceiling with capability of low temperature heating (33–45 °C)

In particular, two technologies can be cited as follows:

1. (1)
   Ventilated facades, which increase the climatic insulation of walls through the use of air cavities with circulating air in communication with interior environment or exterior (Fig. 1 

   Fig. 1

   

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   Original LESP wall and building plant schema

   Fig. 1

   

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   Original LESP wall and building plant schema

   Close modal

   ).
2. (2)
   Radiant acclimatization, which permits the use of low temperature water (Fig. 2 

   Fig. 2

   

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   Seasonal behavior of the proposed wall

   Fig. 2

   

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   Seasonal behavior of the proposed wall

   Close modal

   ) for heating purposes (33–45 °C) allowing great economic and energetic advantages.

High energetic efficiency and passive building concepts have developed to meet very advanced energy performance requirements:

1. (1)

   demand for useful energy for heating ≤ 15 kW h/m² yr

2. (2)

   no thermal bridges

3. (3)

   total primary energy demand ≤ 120 kW h/m² yr

4. (4)

   days with internal air temperature ≤ 25 °C under 10%

LESP panels define a building envelope, which minimizes the heat losses and ensure an improved comfort for people. It includes a thermal shield realized by circulating water, which helps maintaining internal thermohygrometric wellness by low-level and renewable energy sources. It can operate without any energy supply from fossil fuels. This concept allows new directions for designing a new generation of energy efficient buildings with a high comfort level and very low energy consumption.

Zero energy consumption is a very ambitious target for traditional insulated walls. However, LESP walls can easily reach this condition.

The building envelope consists of two essential parts:

1. (1)

   thermal barrier by thermally stabilized water by heat exchanges in the soil at a temperature not near to groundwater temperature

2. (2)

   solar plant on the roof to provide water heating and photovoltaic production

Figure 2 shows LESP concept and identifies the following elements:

1. (1)

   wall

2. (2)

   internal coil for dynamic insulation of the wall

3. (3)

   return pipe

4. (4)

   geothermal heat exchanger

5. (5)

   discharge pipe

6. (6)

   circulation pump

LESP presents an internal barrier, which reduces the heat losses from the building ensuring constant exchanges with a thermal source at almost constant temperature. It aims to keep constant thermohygrometric conditions within the building regardless of climatic conditions and to acclimatize the building without any energy supply by fossil fuels. In many cases, it does not need any external source of energy except water pumping.

This solution can be inserted in a traditional concrete prefab panel [2] and generates the ZEBRA building model (Fig. 2) which has been initially studied.

Different architectures could be more effective, i.e., container building. This paper studies this solution in terms of performances against a traditional competitor.

The traditional wall can be modeled by electrical analogy (Fig. 3). More layers of different material in terms of both nature and thermal properties constitute it.

is the representation of the external and internal adductive coefficients, respectively.

The LESP wall model has an increased complexity when compared to traditional insulated walls. A coil, in which water flows at temperature T₀, governs the heat loss from interior to exterior environment. The thermal profile presents a thermal discontinuity by circulating water at almost constant temperature (Fig. 4).

where the subscript tot indicates the amount of heat subtracted to the water.

This concept presents some similarities with geothermal heat pumps, but has a fundamental benefit: The interior environment exchanges with the water shield nearly at groundwater temperature (almost constant all over the year).

The wall thickness and optimal sizing depends on the materials used and the climatic zone. A careful design of the system allows achieving arbitrary low levels of heat loss from the inner wall and serpentine and is governed by the internal thickness x. it is then evident that the proposed system provides arbitrary insulation and heat losses by varying one dimensional parameter.

Containers have unified sizes. ISO unification allows the following lengths: 10 ft, 20 ft, 30 ft, and 40 ft. International container have a width of 8 ft and height from 8 ft to 8 ft 6 in. European standards for land transport within Europe imposes 2.50 m wide inland container for combined road/rail transport operations. Figure 5 represents a typical container frame.

ZETHa design has designed on unified dimensions, with the goal of simplifying assembly and reducing manufacturing times, minimizing thermal bridges, and adopting a commercial panel for circulating water.

A schema has represented in Fig. 6. It has specifically designed to minimize thermal bridges and limiting them in the corners where are located technological areas hosting principal water pipes (Fig. 6). Reference container houses based on this architecture has shown in Figs. 7.

Energetic performances of ZETHa container house can be evaluated in any specific location. A sample calculation has produced in Bologna (Northern Italy). Climatic data have obtained RETScreen International [6]. Reference temperatures has assumed from Italian and European standards [7–9]. They are as follows:

• internal reference temperature: summer 26 °C; winter 20 °C

• external reference temperature: summer 35 °C; winter −5 °C

A comparison between traditional and ZETHa configuration houses has realized assuming the same wall structure with or without the thermal shield by circulating water (Fig. 8). Calculations have been produced by a certified [10–17] software named termus-g [18]. Table 1 shows the results of the calculations. It calculates thermal transmittance and Glaser diagram of walls, floors and windows. In the traditional case it results an overall thermal transmittance U_wall = 0.435 W/m² K (R_wall = 2.29 K m²/W).

The energetic performance of the building has calculated by energetic certification software docet 2.0 (freeware by CTI/ENEA) [19]. It has assumed a 20 ft container represented in Fig. 7. Windows has assumed with an overall thermal transmittance U = 1.8 kW/m² K.

The following reference data of the building are assumed:

• gross external surface: 75.6 m²

• usable area: 27.0 m²

• gross heated volume: 73.0 m³

• degree days: 2259

• shape factor S/V: 1.04 m⁻¹

• indoor temperature: 20.0 °C

The data in Tables 1 and 2 have calculated. Tables 3 and 4 present monthly results. The average annual energetic values have calculated for 1 m² of net plant area (Table 5).

The general model of the system has shown in Fig. 9. It presents a hydraulic thermal shield where water flows after exchanging heat with the ground. To ensure the best possible distribution of the temperature two metallic sheets have inserted on both sides of the adiabatic panels. They ensure a uniform distribution of temperature for the thermal cut. Main thermodynamic parameters have estimated by Eqs. (3) and (4). Thermal insulation by water acts on lateral and top surfaces, and not on the ground floor. The envelope has modeled assuming different values of the thermal barrier temperature.

Thermal conductivities of the external and internal section of the wall are as follows:

• internal wall: U = 0.7 W/m² K

• external wall: U = 1.32 W/m² K

The effects of thermal barrier have evaluated for different heat barrier average temperatures as follows:

• Winter: Tw = 10 °C; 15 °C; 17 °C

• Summer: Ts = 18 °C; 16 °C; 12 °C

Thermal distribution and Glaser diagram have evaluated. Average thermal exchanges have evaluated, assuming the data reported in Table 6.

Results have plotted in graphs representing the average seasonal heat dispersions and net energy needs of the building in different conditions: Figure 9 describes winter conditions and Fig. 10 summer conditions.

A simple energetic balance allows calculating heat dispersions trough the envelope of the ZETHa building. Water mass flow (and velocity) has evaluated to limit heating and produce an adequate thermal stability of the barrier.

Table 7 presents the results as a function of water average temperature in both winter and summer conditions. The following convention has adopted: Minus means that water must be cooled and plus means that it must be heated to maintain thermal equilibrium.

Optimal energetic conditions have evaluated by the following considerations. The most interesting configuration seems the one with an average exchange temperature of 12 °C during winter and 18 °C during summer. It means that water can be used at groundwater temperature (Fig. 9). Assuming the location of Bologna, average groundwater temperature is about 14 °C. The following maximum temperature variations in water are −1 °C during winter and +1 °C during summer.

It is evident that external temperatures between 12 °C and 18 °C reduce the convenience of the system. This evaluation has derived from the data in Table 8. The comparison of annual thermal needs in Bologna clearly demonstrates the advantage of water thermal shield (Table 9).

It has calculated 0.342 W/m² K for the considered walls in assumed reference conditions.

Energetic exchanges have modeled assuming water velocity about 1 m/s, pipes with diameter of 1 in. (24.5 mm) and daily average work time of 16 h.

Required operative conditions require an average low water velocity (≅0.5 m/s) and ensure quiet operations. The average power for water pumping is about 0.18 kW assuming a conservative efficiency η = 0.8. Overall annual consumption is then about 870 kW h/yr.

A high efficiency heat pump conditioner (Tables 10 and 11) can ensure internal air treatment and supplementary acclimatization. An annual energy consumption of about 650 KW h has estimated. Other energetic needs have been evaluated for domestic uses. Assuming one occupant, the following consumptions have assumed according to European statistics [19]. Total consumptions including appliances, water pumping, and air treatment are about 3.25 MW h/yr. Hot water consumption is about 0.800 MW h/yr according to European standards [10].

Energy production for sanitary use can be produced by solar heating modules, which can be applied on the vertical façade with south orientation. A 6 m² solar thermal plant allows producing about 1.800 MW h.

Considering internal uses and acclimatization consumptions, a photovoltaic plant on the ceiling needs can satisfy overall energy needs. A photovoltaic plant about 3 kW (Table 12) allow to satisfy them entirely. Total photovoltaic production and the thermal production are more than required.

The above results show that the energetic behavior of the ZEBRA building with a thermal shield realized by circulating water is very interesting in terms of energy saving. On the other side the new wall model present also the advantage of increasing human comfort [20]. ASME [21] identifies six factors that affect thermal sensation: air temperature, humidity, air speed, mean radiant temperature (MRT) [22], metabolic rate, and clothing levels. Human wellness is a complex phenomenon [22].

The temperature of internal surfaces (i.e., walls, ceiling, floor, windows) plays a fundamental importance. Cool walls remove radiated heat from exposed skin and clothes. Low or high temperatures of radiant sources have a great influence on the comfort perception [23–25]. The ZETHa building system allows an effective regulation of the indoor MRT, which can be controlled by circulating water inside the thermal shield. In avoids excess of wall cooling during winter, and excess of wall heating during summer.

The ZETHa concept ensures an effective balance between internal temperature and MRT and ensures a more comfortable space. In potentially ensures a higher level of comfort than any other building. Only air ventilation is required for cooling and a very limited air heating is required during winter [19].

where H is the internal heat production rate per occupant and unit area (W/m²), L is energy loss from body (W/m²), and M is the metabolic rate per unit area (W/m²).

PMV and PPD allow an effective calculation of the wellness parameters. Assumed data are reported in Table 13 and PMV and PPD calculations have been reported in Table 14.

Wellness graphic PPD on PMV is reported in Fig. 11 both in summer and winter.

These results allow verifying that internal conditions are very good verifying initial qualitative evaluations by Dumas et al.

The proposed building model presents an effective reduction of thermal needs by design, because of the effects of the water circulation LESP wall. In particular, the LESP wall architecture with a thermal shield by circulating water at groundwater temperature, ensures lower energy consumption and a higher comfort with negligible energy needs by increasing the comfort for occupants.

The presented ZETHa container house presents a low cost, and easily mobile solutions for a comfortable life in any situation when temporary housing needs are required with the maximum internal comfort.

This paper clearly demonstrates that ZETHa allows excellent energetic performances and interior comfort. It demonstrated that it could become energetically self-sufficient by renewable energy (solar heating and photovoltaic electricity).

Further studies are necessary to produce an effective optimization of the container house in terms of walls composition and of plant optimization.

This demonstration of the energetic feasibility opens novel scenarios through an optimization of this building concept. Another objective of future studies relates to optimize the system defining possible applications to cabin of aircraft and of airship especially. In the aeronautic sector, it could open novel scenarios relating to smarter acclimatization systems. Further studies will be also necessary to allow an effective personalization for different operative scenarios and to its industrialization.

Nomenclature

A =

area (m²)

c =

thermal capacity (J/kg K)

h =

thermal conductivity (W/m K)

H =

internal heat production rate of an occupant per unit area (W/m)

L =

energy loss from body (W/m)

LESP =

low exergy structured panel

M =

metabolic rate per unit area (W/m²)

PMV =

predicted mean vote index

PPD =

predicted percentage dissatisfied index

Q =

heat (W)

Q =

heat flux (kW/m²)

S =

thickness (m)

T =

temperature (T)

U =

thermal transmittance (kW/m² K)

ZEBRA =

zero energy consumption building totally renewable addicted

ZETHa =

zero energy temporary habitation

α =

thermal adduttance (W/m K)

λ =

thermal conductivity (W/m K)