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The objectives of this case study is to demonstrate the amount of heating energy saved as well as the level of improved comfort when replacing conventional poorly insulated container offices with modern well insulated modular cabins.
For this study two cabin models with an equal geometry but differing insulation envelop are created. These are used to compare heat transmittance of various elements of the cabin, the heat energy required for a certain comfort level as well as the associated cost and carbon emissions.
It can be seen that the insulation envelope of our conventional cabin has been improved by:
Due to large wall area, reducing the thermal transmittance through walls will have a significant influence on reducing heat loss in temporary buildings. Replacing single glazed windows with double glazed windows will reduce the heat loss through windows by 50%.
Several simulations were run in order to assess the energy savings as well as improvements in comfort involved with the improvement of the insulation envelope of the cabin. The potential energy savings which could be achieved by improving the air tightness of the well-insulated cabins is also investigated.
The table below shoes the energy required for heating both the conventional as well as the improved type of cabin in order to maintain a comfort level of 20°C dry resultant temperature. The following results are obtained from running a simulation for the pre-defined heating season from 01 October to 31 March.
The simulation demonstrates that improving the insulation envelope of the cabins, which are conventionally used for accommodation on construction sites, can reduce the heating requirements by almost 50%.
The infiltration rate for conventional cabin is assumed to be 2ac/h. With an infiltration rate of 1.0ac/h the building can be classified as air tight as a general office according to table 4.1 of the CIBSE Guide A. The table below indicates the annual heat requirements for an improved cabin of different air tightness.
It is shown that improving the air tightness of the cabin by reducing cracks and openings in the façade, the energy required for heating can be further reduced by 39%.
In order to assess human comfort inside both type of cabins the dry resultant temperature and relative humidity inside the cabin has been analysed for a typical winter week. For this study the heaters inside the cabin have been switched off. The figures below compare the results obtained using ESP-r. The lower line in the following graphs shows the external temperature, the upper line shows the dry resultant temperature inside the cabin (Celsius grades)
It can be seen that the dry resultant temperature inside the well insulated cabin is an average 3°C higher than the dry resultant temperature inside the poorly insulated cabin during working hours.
Further analysis has shown there is a larger difference between mean surface temperatures and dry resultant temperature in poorly insulated cabins. This means that workers will experience a higher level of discomfort. The lower line in the following graphs shows the relative humidity inside the cabin (%) , the upper line shows the external relative humidity inside the cabin (%).
It is clearly demonstrated that the relative humidity inside the well insulated cabin is an average 8% lower than inside the poorly insulated cabin. In general it can be said that a maximum room relative humidity of 60% within a recommended range of dry resultant temperatures would provide acceptable comfort conditions for human occupancy and minimise the risk of mould growth and house dust mites. [1] In the conventional cabin this maximum relative humidity is exceeded for a larger period of time than in the improved cabin during working hours.
(1) CIBSE Guide A: Environmental Design
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