590078 Fax: 01420 590073 E-mail: solutions@timbersolve.co.uk

Boise Building Products Ltd
Building 345, Heyford Park, Upper Heyford, Bicester,
Oxfordshire, OX25 5HA
Tel: 01869 238650 Fax: 01869 238660

TECHNICAL BULLETIN No
: 19





ISSUED :

January 2005


Additional Loads: Thermal Stores

Introduction

Changes introduced to The Building Regulations, Approved Document L1 (2002)
Conservation of fuel and power in dwellings have increased the requirements for
the energy efficiency of buildings, including the performance of hot water and
central heating systems. Requirement L1 highlights the need to limit the heat loss
from hot water vessels, to provide hot water systems which are energy-efficient,
and to provide information and services which enable the building occupier to
maintain the system in such a manner as to use no more energy than is
reasonable in the circumstances. These changes place a greater emphasis on
the overall system control and performance, thus giving rise to the development
of products that are able to meet the required levels of efficiency.

The fully integrated Thermal Store as shown in Figure 1, presents a method of
providing a more centralized and integrated hot water and central heating system.
The industry claim numerous benefits over the conventional hot water cylinder
and cold water storage tank arrangement, however it is the energy efficiency of
the product which has given rise to the increased use of thermal stores in new
build house construction. Thermal stores combine the hot water cylinder and
cold-water tanks into one convenient and
efficient water store. This arrangement places
increased load on the supporting floor.
Thermal stores are produced in various
capacities with full weights ranging from about
170kg to 280kg, by comparison, a typical
conventional hot water cylinder weighs only
110kg (this latter load is accounted within the
1.5kN/m
2
imposed load normally allowed for
in the domestic dwellings). So it is important
that the increased load from thermal stores is
recognized and accounted for by the Floor
Designer.








Figure 1. Thermal Store


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, 4 Lenten Street, Alton, Hampshire, GU34 1HG
Tel: 01420 590078 Fax: 01420 590073 E-mail: solutions@timbersolve.co.uk
The aims of this Technical Bulletin are firstly to illustrate how to calculate the
applied load from thermal stores and how to apply this additional load to the floor
scheme, and secondly to show a method of detailing the floor directly below the
thermal store so as to distribute the load uniformly.

It is important that the developer provides to the floor designer all information
about the thermal store at the time of quotation. If no specific manufactures
model number is available, then the full capacity and the actual base footprint
area of the store are required by the floor designer. It is suggested that the load
allowed for the thermal store is shown on the quotation drawings.


Thermal Store Load Calculation and Application

The following example is based on the applied load from a Gledhil BoilerMate
2000 BM 185 thermal store which has a weight when full of 215kg, and a base
footprint of 595mm x 595mm. The BCI-Joist floor has been designed with a load
of 0.75kN/m
2
(dead load, long term) + 1.5kN/m
2
(imposed load, long term).

Firstly, calculate the total load of the thermal store.

(Weight) (Gravity) (Load)

215kg x 9.81/1000 = 2.1kN




Ans (A)


Next, calculate the total imposed load which has been allowed on the floor.
(Area)

(UDL)
0.595m x 0.595m
= 0.35m
2
x 1.5kN/m
2
= 0.525kN

Ans (B)
(If the thermal store has a cylindrical footprint, assume that it is a square with
each side equal to the diameter)

Next, calculate the additional load to be applied to the floor


Additional Load
= Eqn (A) - Eqn (B)



= 2.1kN - 0.525kN
= 1.575kN

Ans (C)

So, the additional load that needs to be applied to the floor in the area of the thermal
store is 1.575kN. It is unlikely that the floor decking will adequately support the total
2.1kN load of the thermal store, so it is necessary to consider either adding trimming
member within the floor, or specifying adequate spreaders on top of the floor deck to
distribute the load evenly into the floor joists. The number of trimming members to
include within the floor scheme is based on the size of the footprint of the thermal store
as shown in Figure 2. The extra load to be added to the floor joist design is shown in
Figure 2 as four
red
dots, each red dot represents a point load of 1.575/4kN = 0.394kN.
The individual point loads of 0.394kN should be apportioned into the adjacent joists
relative to the distance between the location of the point load and the joist. Apply the
additional loads to the BCI Joist floor design, and indicate the magnitude of the loads
allowed on the quotation drawings.





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Provided under exclusive arrangement by
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, 4 Lenten Street, Alton, Hampshire, GU34 1HG
Tel: 01420 590078 Fax: 01420 590073 E-mail: solutions@timbersolve.co.uk
Figure 2. The position & number of additional loads dependant on the size of the
thermal store footprint. Position loads 100mm from the extent of the footprint.