Convention 6.15 - Bivalent system proprtioning within a building zone

Where a bivalent system i.e. 'One in which the heating is supplied by two (or more) different types of heatsource' is present in a zone within the building under assessment, entries are required to specify theproportion of load met by each of the systems present. This must be determined on a 'zone by zone' basisi.e. the same HVAC system can only be assigned to multiple zones when the source(s) and deliverymethod(s) are the same. The Assessor is required to enter the proportion of heating load that the additional(bivalent) heat generator(s) provide and the balance is assigned to the main system.

When a bivalent system is entered the Assessor can apply any control corrections to each of the systemefficiencies as appropriate. It is only however possible to select one set of control options. These should be selected as appropriate to the system which supplies the greatest heating load.Any system which provides cooling must be entered as the main system. When none of the systems providecooling the main system should if possible be the one which supplies the greater proportion of heating load.

1. The software will only account for cooling from the main system and the main system does not needto be the one which supplies the greater proportion of heating load in this instance.

2. Where there is evidence of the relative heating load e.g. a 'heating load design' this should be used.

3. Where the relative heating load is unknown the following principles shall be applied:

a) One central (multi-zone system) and one or more local (single zone) system(s):- 80% is assigned to the central system and 20% to the local system (or equally divided between the localsystems).

b) Two central (multi zone) systems only:- 50% is assigned to each system.

c) Two central (multi zone) systems and one or more local (single zone) system(s):- 40% is assigned to each central system and 20% to the local system (or equally divided between the localsystems).

d) No central (multi zone) system and two or more local (single zone) systems:- load is equally assigned to each local system.

For the purpose of this convention a split or multi split is considered to be a local system.