Mechanical and Misc. Modelling Norms

DCH BRICK 1.2 conventions for Mechanical systems, equipment and modules.

Terms

MAY: condition is permitted SHOULD: condition is recommended if possible MUST: condition is required MUST NOT: condition is forbidden

HVAC Units

1. HVAC units such as AHUs and FCUs MUST be modelled with the sub-equipment that make up those units. This may include Supply and Return Fans, Heat Exchangers, Valves, Filters and Dampers.

2. The sub- equipment of HVAC units MUST be modelled as brick:isPartOf the parent HVAC unit.

3. Points that relate directly to HVAC sub-equipment MUST be mapped to the sub-equipment.

4. HVAC unit points that relate to the unit but not to sub-equipment MUST be mapped to the parent HVAC unit.

5. If a point is labelled as relating to a HVAC unit by name but is a measurement or SP of a room/zone temperature/RH/CO2, then that point MUST be mapped to the relevant location.

6. Points that relate to HVAC switches MUST be mapped to the HVAC unit not to the location that they are located.

7. If an HVAC Zone exists, then the HVAC unit brick:feeds to that Zone. Rooms are then brick:isPartOf that zone. If no HVAC Zone exists, which is likely the case for an FCU feeding to a single room, then the HVAC unit brick:feeds to that room directly.

8. If an HVAC unit has points related to valves such as Chilled/Hot Water, Chilled and Hot Water Coils (brick:Chilled_Water_Coil and brick:Hot_Water_Coil) MUST be created as ‘isPartOf’ the HVAC unit whether there are points associated with the coils or not as these form part of the fluid path for building water systems.

9. Chilled Water and Hot Water that supply water to heat exchanger coils in HVAC units MUST brick:feed to the heat exchanger components that are part of the HVAC unit, not to the HVAC unit itself.

10. If an HVAC unit has known sub-equipment but no points associated with that sub-equipment, the modeller MAY include that sub-equipment as part of the parent unit, except in the case of water coils (see rule 8).

HVAC Zones

1. The air side of HVAC equipment MUST relate to locations or other equipment by the brick:feeds relationship. Brick:feedsAir relationship is not used in DCH.

2. If a HVAC Zone exists, the HVAC unit MUST feed the relevant zone.

3. A brick:HVAC_Zone MUST be located by brick:hasLocation to a location.

4. A HVAC Zone MAY be one space or contain several spaces which have conditions controlled by a single or numerous HVAC units.

5. A room MAY be the location of multiple HVAC Zones.

6. A brick:Average_Zone_Air_Temperature_Sensor MUST be mapped to the zone.

Return Air and Exhaust Fans

1. DCH prohibits locations feeding equipment. This is circumvented by creating Air Plenums in particular situations.

2. If an exhaust fan exhausts air from multiple rooms, brick:Air_Plenum MUST be created as brick:isPartOf those rooms.

3. Air Plenums MUST brick:feed the exhaust fans.

4. If an exhaust fan only exhausts air from a single room, the exhaust fan must have a brick:hasLocation relationship with that room.

5. If a HVAC unit has a return air path, a brick:Return_Air_Plenum MAY be modelled in the same manner as exhaust fans by locating a brick:Return_Air_Plenum in the relevant location(s). The brick:Return_Air_Plenum MUST brick:feed the HVAC Unit. If no points are associated with a return path (other than those Return points that can be associated with the HVAC unit) then it will likely not be necessary to model a return plenum.

Outside Air to HVAC

1. Outside Air paths are not modelled by plenums, these are assumed to exist with the modelling of ‘Outside_Air’ equipment in the HVAC unit such as brick:Outside_Air_Fan and/or brick:Outside_Air_Damper.

HVAC Mixed Air Temperatures

1. If in the situation of an HVAC unit which contains multiple mixed air temperature sensors and an average point of those sensors, the point which is the average of those sensors MUST be classed ‘Mixed_Air_Temperature_Sensor’, the other individual mixed air temperature sensor points SHOULD be classed as ‘Air_Temperature_Sensor’ or not included in the model.

VSDs

1. If a VSD is to be included, it MUST be modelled as part of the associated equipment. For example, AHU01_SupplyFANVSD brick:isPartOf AHU01_SupplyFan.

Sensors as Equipment

1. Sensors (which includes IoT sensors) MUST not be modelled as equipment

2. Sensor output data is modelled as a point and MUST be mapped to the relevant equipment, location or system. E.g. THLM IoT sensors must be modelled to be located where they are physically located, but the Air_Temperature_Sensor of the sensor MUST be point of the location directly. I.e. “THLM sensor A” brick:hasLocation “room A”, “THLM sensor A temperature” brick:isPointOf “room A”.

Systems

1. Systems are used to group equipment. This SHOULD be for the mapping of point that relate to the system that cannot be mapped to equipment within the system, this may include heating schedules, heating demand or in some cases supply and return temperatures (*see note).

2. Examples of systems are:

   • Chilled Water System

   • Hot Water System

   • Domestic Hot Water

3. For example, a Hot Water System may consist of:

   • Boilers

   • Pumps

   • Valves

   • Storage

4. The mapping of points to systems and the equipment in systems is analogous to the mapping of points in HVAC units and their sub-equipment.

5. Hot/Chilled Water coils that are part of HVAC units MUST NOT be grouped in a system, they MUST remain part of the HVAC unit.

NOTE: The mapping of Supply and Return Temperatures may depend on the system. For a system with a single chiller, supply and return temperatures may be more appropriately mapped to the Chiller as this is the only source of thermal exchange. For systems with multiple chillers or other sources in the same system such as storage tanks, it may be more appropriate to map the supply and return temperatures to the system model instance. For systems with multiple loops, it may be more appropriate to map to the relevant loop (see next section).

Loops

1. Some buildings may have physical water loops for chilled/hot/domestic water. These loops may be distribution for various equipment around the building, often these loops are connected by heat exchangers, storage tanks, or header tanks.

2. Pipework MUST not be modelled as pipework is represented by the ‘feeds’ relationship.

3. As in the same case with systems, it may be necessary to add loops to the model to enable specific points to be mapped to those loops that cannot be mapped otherwise to equipment. Loops also add increased clarity as to where equipment sits in a water distribution system.

4. Heat Exchangers that transfer energy between loops MUST be modelled as being part of each loop.

5. Equipment within each loop also SHOULD be grouped as part of the system as a whole.

6. Points that MAY be mapped to loops include ‘Differential Pressure’, ‘Supply Water Temperature’ and ‘Return Water Temperature’.

   • In the below diagram two hot water loops are shown, the PrimaryLoop and the SecondaryLoop.

   • Supply and Return Water Temperatures do not relate to a single piece of equipment as they are feeding multiple AHU Coils. Therefore they are mapped to the Secondary Loop.

Weather Stations

1. Many sites have points relevant to the weather conditions. However, the site may not have a specific weather station, or it may not be known if one exists from the site information.

2. A ‘virtual’ weather station MAY be created to map these points to.

3. However, if the weather point is specific to a location or known to be in a location, then that point SHOULD be mapped to that location rather than to the weather station.

4. From the below example weather points exist within the points list obtained from the BMS yet no further information is known, therefore these points are mapped to a ‘Weather_Station’. It is known in this case that a Weather Station exists located on the Building Roof. Other buildings may not have weather station location information, in those cases the weather station SHOULD be located (brick:hasLocation) on the building.