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Analysing the real building and the Actual Building

The preceding sections of this user guide describe the approach to analysing the real building, using simulation methods tailored to the detailed representation of systems.
 
In order to comply with the special requirements of NCM a modified approach is required. This involves analysis of the Actual Building and the buildings which the software derives automatically from it – the Notional Building and (for EPC purposes) the Reference Building. These analyses are performed in the VE Compliance view of the VE, where tools are provided to facilitate the input and editing of the additional data items.
Because some of the data required for NCM is shared with the analysis of the real building, NCM analysis should be conducted on a copy of the real building model modified to accommodate the NCM requirements.
 
In the VE Compliance view the Monodraught HVR units and logos are not displayed, and their place is taken by provisions compatible with the NCM rules. In this view, it is not possible to modify the assignment of rooms to unit groups. The Assign Room Group window will notify you when this is the case:
Fan heat gains from Monodraught HVR systems will be ignored in NCM analyses, which use standard prescriptions for room heat gains. The electricity consumption of the ventilation fans, must, however, be accounted for.
 
To represent Monodraught HVR systems working in combination with the systems providing heating (and where appropriate cooling) to the building, one or more Apache Systems must be created. The characteristics of these systems should be entered via the UK NCM system data wizard, starting with the selection of a suitable system type from the UK NCM system type menu. Adjustments should then be applied to cater for the unique features of the Monodraught HVR systems.
 
To cater for rooms for which a Monodraught HVR system supplements an air conditioning system, an Apache System should be created with an appropriate air conditioning system type, and in this case Changeover mixed mode free cooling on the Apache System Cooling tab should be set to Mechanical ventilation.
Close attention should be paid to the settings on the System adjustment, Metering Provision and System controls tabs of the UK NCM system data wizard, since these have a critical effect on performance as assessed by the Regulations.
 
When the Apache Systems have been created, they must be assigned as appropriate to each room served by a Monodraught HVR system. These assignments can be made (to the System field on the System tab) either in the Building Template Manager or in the room’s Space Data dialog.
 
On the System tab of the Room Data dialog for each room served by a Monodraught HVR system:
-        System and Auxiliary vent. system should be set to the appropriate Apache System.
-        DHW system should be set to the Apache System created for this purpose.
-        Free cooling flow capacity should be set to the maximum volume flow rate that the Monodraught HVR system is able to deliver to the room.
-        Is there mechanical supply in this room? (when present) should be ticked, and immediately below it the checkbox Specific fan power should be set according to the principles described below.
-        Demand controlled ventilation Type should be set to Demand control based on occupancy density (Cd = 0.85).
 
For heated-only rooms served by Monodraught HVR systems, Cooling/vent. on the Cooling tab should be set to Mechanical ventilation. In cases where the Monodraught HVR system provides all the ventilation, the Air supply setting on the Ventilation tab of the UK NCM system data wizard should be set to Local ventilation-only units, such as window/wall/roof units serving a single area. The natural ventilation component of the system will be taken into account via SFP adjustments described below. It should be noted that the aspects of the system which provide benefit in the form of reduced summertime temperatures do not explicitly receive credit for this benefit under the current NCM Criterion 3 rules, which in contrast to earlier editions of the Regulations are expressed exclusively in terms of reduced solar gain. However, this aspect of performance will form an important part of the design as assessed by the performance of the real building.
 
Set up this way, the system will be assessed for regulatory purposes against a comparable system in the Notional Building.
Fan power used by a Monodraught HVR system is represented within the NCM framework as a component of auxiliary energy. This is the sum of contributions from pumps and fans. Pump power is a function of system category and subject to limited user control. Fans fall into two categories – central and local – for each of which a specific fan power (SFP) must be specified.
 
In the case of heating-only systems for which ventilation is provided locally the SFP parameter on the Apache System dialog (System specific fan power (SFP)) should be set to zero and a suitable SFP value entered on the System tab of the Room Data dialog for each room. This value should represent the average SFP applicable to the room ventilation during operating hours, accounting for the fact that for many hours the fan will be off. A suitable value (which will typically be very small) should be derived from detailed simulations performed (under equivalent assumptions) for the real building.
Where heating and cooling is supplied by a separate system providing mechanical air distribution there will be SFPs associated with the central system and/or the local air delivery. Where appropriate these SFPs should be modified to take account of the small additional fan power incurred by a Monodraught HVR system.
A separate Apache System, with suitable operation parameters, should be created to provide domestic hot water (DHW), and assigned to the rooms for this purpose.
 
For the model used for NCM analysis, infiltration is set using parameters on the Building & System Data dialog. MacroFlo analysis should be disabled by ensuring that the MacroFlo link? checkbox is unticked on the Simulation Settings tab of the Building & System Data dialog.
 
On the Simulations Settings tab of the Building & System Data dialog (accessed via the button Set Building & System Data at the bottom of the screen):
SunCast link? should be ticked if a suitable shading file has been generated.
MacroFlo link? should be unticked (in contrast to the setting in Apache View).
HVAC link? should be unticked (in contrast to the setting in Apache View).
Radiance link? should be unticked.
Natural ventilation air exchange? should be unticked.
 
With regard to the numerous other data inputs relating to NCM presented in the VE Compliance view, reference should be made to the general guidance provided on this aspect of the software.