Reference Building Form
Under the 2008 regulations the Reference building generally had a lot of glazing. A typical building would have up to 40% of the external wall area glazed and 20% of the Roof area assigned rooflights.
In the 2017 regulations spaces are categorised as either Side-Lit, Roof-Lit or No glazing based upon the NCM activity. Spaces in the 2017 Reference building will have either windows or rooflights but not both.
Side-lit: e.g. Offices, circulation, etc.
Roof-lit e.g. Warehouse spaces, etc.
No-lit: e.g. Voids, plant, cinema, theatre, etc.
Windows within the 2017 Reference building will form a strip across the whole facade that’s either 1.5m tall or 40% of the Surface area, whichever is the lesser of the two.
The 2017 Reference building will have considerably less glazing than in the previous regulations. As a result fabric losses will be lower resulting in lower heating loads and Solar gains will be lower resulting in lower cooling loads.
Building Fabric & Air Permeability
The fabric properties used by the Reference building are much lower than even the fabric standards. It may be that designers need to target this level of insulation in order to obtain a pass rating.
If the Actual Building design is poorer then the difference in performance will need to be made up elsewhere.
As well as having improved U-values, Air permeability in the Reference Building has halved to 5 m3/m2 @ 50 Pa, so the Reference will incur less infiltration heat loss.
So although the actual building limits have not altered significantly, the aim is still to approach these new Reference building figures to achieve compliance.
Lighting
Under the 2008 Regulations the Reference Building used a fixed Lighting power Density (LPD) of either 3.75 W/m2/100 lux or 5.2 W/m2/100 lux depending on the assigned activity.
This was criticised as it was much tougher to achieve these levels in smaller spaces.
In the 2017 regulations, a lighting power curve dictates the LDP for the Reference building. This curve is intended to be representative of a lighting system with an efficacy of 65 Lummens/Watt.
Larger, open plan spaces will have much lower LPD’s than previously however smaller spaces may have a less onerous target.
In addition to the Reference building using more efficient lighting, many spaces will also incorporate photoelectric dimming control further reducing lighting loads in the reference building.
So the balance between solar gain and shading effects on dimming are very important and this means introducing Suncast and Radiance into a DSM simulation is now more valuable.
So designers need to work closer with lighting engineers to collate these figures.
Fuel Factors
For Part L 2017 the only major change with fuel factors was the reduction for both Grid Supplied/Displaced Electricity from 0.643 kg.CO2/kWh to 0.323 kg.CO2/kWh
Reference Building Systems
Reference Building System efficiencies on the whole have increased. Most notably DHW, Cooling and Heat Recovery Effectiveness.
Demand Control Ventilation
For Part L 2017 you will find an option for Demand Control Ventilation (DCV) at room level.
Zones with demand controlled ventilation (DCV) can be specified using Room Query.
Having DCV will reduce the volume of fresh air being supplied subsequently reducing heating loads and fan energy subsequently reducing auxiliary energy.
Air flow regulation is by either speed or damper control.
Also there is an enhanced ventilation control for natural ventilated spaces which is following the same approach of varying the fresh air supply so the same effects on heating load will be expected.
Auxiliary Energy
The Auxiliary Energy method under the 2017 regulation is much clearer than under the previous regulations.
Auxiliary energy will be automatically calculated based upon:-
The selected NCM System type (via NCM wizard)
The SFP for the System (now more guidance on SFP’s)
The pump type selected (Constant Speed, Variable Speed)
Terminal Units SFP
Peak Heating/Cooling loads (performed automatically during Simulation)
Demand Controlled Ventilation – at room level, shown in later slide.
Room Extract Systems
See the modelling guide paras 74-90 for details on pump and fan power densities, including tables.
Solar Gain Check
Under the 2017 regulations a limiting solar gain check is performed where the aggregated solar gains between April and September must be below a Benchmark.
Key change is that all regularly occupied spaces need to comply with this credit regardless of the space conditioning type.
Benchmarks are predetermined using Dublin as the location. Side lit spaces will be based upon the exposed perimeter of the zone and roof-lit activities will be determined from the floor area.
Note that this benchmark is not based on or determined by Solar Gain in the Reference Building, but instead using the method described in the modelling guide paragraphs 91-101.
Through setting up the benchmark model as described in the modelling guide we have determined the following benchmark solar gain for the three cases.
Side-lit space: 190.6644 kWh per meter of exposed facade length
Side-lit space (no exposed facade): TBD
Roof lit: TBD
(Note these are not official published values, just the result of an attempt to back calculate the hardwired benchmark values contained in SBEMie determined by the developers at BRE on behalf of SEAI).
Other changes
Renewables present in the reference building
For 2017 the MPCPC has increased from 1 to 1.15, but the greatly improved Reference Building makes meeting this more challenging.
New treatment for indirectly conditioned spaces
Revised NCM Activity Database for both building types and activity. Example changes include classrooms being rebranded as “Teaching areas”, the removal of cellular and open plan offices so that there is now only a standard “Office” activity and the inclusion of “Misc. 24hr Activities” which cover data centres, server rooms and heavy plant spaces.