Featured Article
| Sustainability in store |
Little did we know when campaigning for the Fingal energy standard in 2005-06 that Construct Ireland would have a direct impact on Ikea’s first Irish store. Driven by a combination of Fingal’s requirements and their own renewable energy policy, the Swedish retail giant has invested in the largest ground source heat pump installation in Ireland and the UK, along with a well-thought biomass system fed by an onsite waste stream and a host of other green measures, as John Hearne reports
|
|
Read More >>
|
Latest Blog Comments
Official magazine of Easca  |
|
Page 1 of 5
Thermal mass can significantly influence a building’s space heating
requirement – in some cases the effect is to increase it, and in others
to reduce it. Leading energy consultant Ciaran King of Emerald
Energy explains how this occurs, and by describing an assessment of the
topic, provides some rules of thumb regarding when thermal mass may be
beneficial, and when it may be detrimental.
The term thermal mass is used to refer to a building’s capacity to store heat within its external insulation envelope. A more precise term is internal heat capacity. To give a few examples, in a masonry cavity wall with insulation in the cavity, the inner leaf contributes thermal mass, but the external leaf does not. Likewise, if a concrete ground floor has insulation under the slab, the slab contributes thermal mass, but if the insulation is over the slab, it does not. Internal walls of dense concrete will contribute significantly to the building’s thermal mass, but lightweight stud partitions will not.
A building’s internal heat capacity can affect its space heating requirements in the following two ways. Firstly, a building with higher heat capacity will cool down more slowly outside of heating periods, and will hence have a higher mean internal temperature. This will tend to increase the space heating requirement. Secondly, a building with higher heat capacity will make better use of internal and solar gains, which will tend to reduce the space heating requirement.
These two effects are pulling in opposite directions, and the question of whether increased heat capacity in a dwelling is beneficial or detrimental depends on which is the more important in the particular circumstances. Factors affecting their relative importance include the building’s insulation level, the amount of heat gains and the occupancy patterns.
The first effect above is fairly clear, but the mechanism of the second merits further explanation. When a building receives internal or solar heat gains outside of heating periods, its internal temperature will rise above what it would otherwise have been, increasing the rate of heat loss. Likewise with gains received during heating periods, provided they are sufficient to raise the temperature above its set-point. In a light-weight building of low heat capacity, the temperature rise will tend to be greater than in a heavy-weight building, and this will drive increased heat loss. Therefore, in the heavy-weight building, the heat gains will tend to remain within the building for longer, where they can make a greater contribution to subsequent heating requirements.
The effects of thermal mass on a building’s space heating requirement are complex, and may depend on factors such as the location of the thermal mass, its exposure to sunlight, and interactions with a slow-response or poorly-controlled heating system. So the assessments described below shouldn’t be regarded as comprehensive.
Base case building
The building used as the base case for the analysis was a typical two-storey semi-detached house just complying with the current building regulations. The internal temperatures, heating schedule, and internal gains assumed were as given by SEI’s DEAP software. Three categories of thermal mass – corresponding to the DEAP thermal mass categories of the same names – were considered as follows:
The constructions used were typical of those in common use, and are described in table one. Note that the lightweight external wall in this table could be either a masonry wall with internal insulation or a timber-frame wall. In the analysis, an allowance was also made for the thermal mass of dwelling contents.
Table 1: Constructions used in the analysis
<< Start < Prev 1 2 3 4 5 Next > End >>
|
|
Issue 1, Vol 5 Out Now
The new look issue of Construct Ireland is available now. Click here to subscribe online and have the latest issue delivered to your doorstep
|
