Space Data (actual & notional building)

Each room has a set of attributes that describe conditions within it. This data, known as Space Data, provides input to the thermal analysis programs. In the <VE> Compliance view, Space Data is divided into six categories:

·       General – Room name and ID, Templates, floor area and volume data

·       Building Regs – room attributes for Building Regulations compliance checks

·       Room Conditions – heating and cooling set points and room thermal modelling settings

·       System – parameters describing the system serving the room

·       Internal Gains – Specification of internal gains to the room

·       Air Exchange – Specification of infiltration, natural ventilation and mechanical ventilation

For most thermal applications, a single set of Space Data applies to each room. However, for Part L (2010) the picture is complicated by two factors:

1.       Special room conditions are stipulated for Part L2 (2010) compliance analyses.

2.       There is a notional building which has room conditions that differ in some respects from those in the actual building.

This section deals with the conditions in the actual building. Here, certain room conditions are taken from data entered by the user (these are often specified by means of a Room Template), and others are dictated by the conditions laid down in the NCM methodology for the particular building type and activity applying to the room (in the main these are taken from an ‘NCM template’).

Each tab of the Space Data dialog must be considered separately to gain a full understanding of the way the NCM rules are applied. The basic content of the Space Data tabs, and the procedures for editing it, are described in the <VE> Compliance and Apache User Guides, as these features are common to all thermal applications and Regulatory Frameworks. The exceptions and special rules applying to Space Data in Part L2 (2010) are described below.

With one exception, data displayed on this tab is the same for all thermal applications. The exception is the NCM Template, which is displayed only for Part L 2010.

NCM Template

The template automatically assigned to the room as a function of its ‘activity’ (see Building Regs tab) to specify those aspects of Space Data that are dictated by the NCM methodology for use in L2 (2010) compliance simulations.

The content of this tab varies with the Regulatory Framework, so is covered in its entirety here rather than in the <VE> Compliance User Guide.

Include room in Building Regs analysis?

Tick this box to include the room in the building regulations analysis. By switching off rooms using this box you can perform separate analyses on different parts of the model.

Simulations in <VE> Compliance will include only the rooms that have this box ticked. If an included room is adjacent to an excluded room, or a room in an inactive layer, the adjacency is treated as a ‘reflexive boundary condition’, which means that conditions in the adjacent, non-included, room will be assumed to be the same as in the included room.

Type of room

This setting determines how the room will be treated for Part L2 (2010). The options are as follows:

·       Heated or occupied room – the usual designation, applying to all occupied spaces within the insulated building envelope (whether they are directly served by heating plant or not). Spaces of this type must be assigned an NCM activity, and will be treated as heated for the purpose of the Part L analysis.

·       Unheated roof – assign this type to a ‘cold’ roof space that has insulation at its base (ie at ceiling level). Rooms assigned this type will not be explicitly modelled in the notional building but incorporated in the elements linking the unheated space with adjacent conditioned spaces.

·       Glazing cavity – windows, rooflights & doors connecting heated rooms with this space will be treated as external. This type is included to cover cases where a glazing cavity is treated for modelling purposes as a separate space.

·       Other buffer space – this room type applies to spaces such as car parks, unheated stairwells and other spaces that form a buffer between the conditioned areas of the building and the outside. This type should only be assigned to spaces lying outside the insulated building envelope. Rooms assigned this type will not be explicitly modelled in the notional building but incorporated in the elements linking the unheated space with adjacent conditioned spaces.

·       Internal void or warm roof – this room type applies to ceiling and floor voids, and to ‘warm’ roofs – those with insulation at rafter level. This type should be applied to unheated, unoccupied spaces that lie within the insulated building envelope.

 

Note: Where a space is subdivided for simulation purposes into separate levels connected by holes there are 3 possible approaches to the assignment of ‘Type of room’:

a) Combine all the levels into one space.

b) Assign the upper levels the same type of room and activity as the occupied space at floor level. They will then be heated and ventilated like that space, but will not receive gains because their floor area will be zero.

c) Assign the upper levels the type ‘Internal void or warm roof’, so that they will be unheated.

 

A drawback with option c) is that in the notional building air exchange between the levels will not be modelled so there will be unrealistic thermal barriers between them. Options a) and b) are therefore preferred.

External ventilation rate (air changes per hour)

This parameter applies only to rooms of type unheated roof space, unheated buffer space and glazing cavity. It is used for the calculation of effective U-values through the space from adjacent heated spaces using BS EN ISO 13789:1999^[7]. These U-values are used in the Part L2 Criterion 2 checks.

Template NCM building type

An efficient way to set NCM activities for rooms is to set the activity in the Room Template. The activity will then be automatically set, along with other Room Template attributes, for all rooms to which the template is assigned. If the selected room has an NCM activity set in its Room Template, the building type associated with that activity is displayed here, provided that it matches the building type set for the model in Building Settings. In other instances, the Template NCM building type box displays the text ‘Unset or incompatible’.

For unheated rooms (those with Type of room set to anything other than Heated room), the NCM activity is undefined and is not displayed.

NCM activity

Each heated room (defined as a room for which Type of room is set to Heated room) must be assigned an NCM activity. This defines the standard operation pattern of the room for the purpose of L2 (2010), which is defined by attributes on the various Space Data tabs. The assignment of these Space Data attributes is effected by the NCM template corresponding to the activity.

Each NCM building type has a predefined list of NCM activities available to its rooms. Once the model building type is defined in Building Settings, the associated activities will be available to heated rooms in the building and can be assigned using the NCM activity attribute.

It is recommended that the NCM activity is set in the Room Template. This saves work as it means that the activity will be automatically set for all rooms assigned that template. An NCM activity is only meaningful in the context of a building type, so this, too, must be set in the template. If no activity is specified in the template the room’s NCM activity will revert to the default activity for the model building type.

If the NCM activity is set in the template, and is compatible with the model building type, it may (like other template settings) be overridden in the room by un-ticking the Template check box and selecting an alternative activity from the drop-down list.

For unheated rooms (those with Type of room set to anything other than Heated room), the NCM activity is undefined and is not displayed. In this case a special NCM template called ‘NCM unheated space’ is automatically assigned to the room.

In Part L2 (2010) certain Space Data settings are under your control (via the room template, which may be overridden in individual rooms) and others are set automatically by the NCM template. This is explained in the context of each of the Space Data tabs in the sections which follow. A brief account of the data used to populate the various tabs appears on the tab title bar.

High pressure drop air treatment

NCM lighting data - Button

This button opens the dialogue NCM lighting data , to adjust settings

All the data on this tab is taken from the NCM template and cannot be edited.

This data specifies the set points and profiles for heating and cooling and the hot water consumption rate.

All the data on this tab is under your control. It is shared with other <VE> views such as Apache View and other Regulatory Frameworks within <VE> Compliance. In particular, the room should be assigned an Apache System with properties accurately describing the system proposed for the actual building.

The following System tab attributes that would normally appear in the ‘System outside air supply’ frame are, however, hidden from view in Part L2 (2010):

·       Flow rate

·       Variation profile

The reason is that a specification of scheduled minimum ventilation forms part of the standard room conditions associated with the NCM activity (which is handled via data on the Air Exchange tab). To avoid a double specification of minimum ventilation the System tab ventilation parameters are disabled in Part L2 (2010).

Ventilation & Exhaust

Mechanical supply

This option becomes active, when the Apache System serving the room has Cooling/mechanical ventilation mechanism set to ‘Mechanical ventilation’. In other cases this is disabled.

Mechanical exhaust

This option allows setting mechanical ventilation for the selected zone. Specify the Exhaust flow rate together with the Specific fan power.

All the data on this tab is taken from the NCM template.

Unlike the NCM template data on the Room Conditions tab, however, aspects of this data may be edited in certain circumstances.

The NCM activity room conditions specify levels and schedules (profiles) for internal gains and (where relevant) electrical consumptions associated with lighting, equipment and occupancy. These gains are automatically set on the Internal Gains tab as a function of the NCM activity.

Lighting gains and consumption, however, are a special case. The NCM activity specifies lighting levels in terms of lux. In the NCM template these are translated to W/m² using a fixed conversion factor – the luminous efficacy. The value of this factor depends on the activity. It is 3.75 W/m² per 100 lux for office, storage and industrial spaces and 5.20 W/m² per 100 lux for other spaces. If the luminous efficacy of the lights in the building differs from the figure assumed in the NCM activity, it is permissible to change the W/m² values for lighting gains appearing on the Internal Gains tab. It is also permissible to change either the W/m² values or the lighting profile in cases where there are controls which dim the lights when daylight is available. In this instance the dimming profile modulating the lighting gain may be replaced by a user-defined formula profile.

Data on this tab is partly taken from the NCM template and partly user-supplied. The rules are as follows.

The NCM activity specifies a minimum ventilation regime for the activity in terms of a flow rate and a profile. This appears as an air exchange of type Auxiliary Ventilation, taken from the NCM template. The NCM minimum ventilation regime applies to all heated rooms, whether air conditioned, mechanically ventilated or naturally ventilated.

Auxiliary ventilation assigned to the room by the user (via the room template or room-specific assignments) is automatically removed. This is to avoid a double-specification of minimum ventilation requirements.

All other air exchanges set by the user – those of type Infiltration and Natural Ventilation –are retained. These are shared with other <VE> views and other Regulatory Frameworks within the <VE> Compliance view, and any edits to them will be reflected in those places.

These rules mean that in models for which a Part L2 (2002) analysis is anticipated, care is needed in ventilation settings. Minimum (‘fresh air’) ventilation must be specified in the form of either auxiliary ventilation air exchanges or system outside air supply parameters on the System tab. It will then be automatically removed for the L2 analysis and will not feature twice. Infiltration should be included at a rate characteristic of the building leakage – that is, with no allowance for window opening or trickle vents. Any natural ventilation introduced for cooling purposes should be modelled in one of the following ways:

a)       using Natural Ventilation air exchanges controlled by formula profile

b)      using the free cooling parameter on the System tab, or

c)       using MacroFlo.

Further guidance on ventilation settings in <VE> Compliance simulations is provided in Appendix A.

 

In the notional building, all data, including Space Data, is set automatically. Space Data is set using the NCM template, with the exception of data on the System tab data, where the following rules apply.

Depending on the type of conditioning assigned in the corresponding room of the actual building (as specified by the Cooling Mechanism parameter for the rooms Apache System), the notional building room is assigned one of three standard Apache Systems:

·       NCM notional heating + nat vent system

·       NCM notional heating + mech vent system

·       NCM notional air conditioning system

These systems are set up with attributes specified in the NCM methodology document^[3].

For rooms without air conditioning, a free cooling ventilation allowance of 5 ach is made in the notional building. This is to avoid the extreme overheating that would otherwise result, which would have an effect on heating loads at other times in the daily cycle.