Nathan McGregor, Bennett Freehill’s BIM Manager, recently completed his MSc in Renewable Energy and Energy Management at Ulster University, and in this bulletin he gives us an insight into his research project : A critical analysis of low carbon design strategies in new buildings.
The research project investigated various low and zero carbon construction options for a case study student accommodation block in Northern Ireland, with an emphasis on achieving Passivhaus Premium standards.
By exploring existing as built case studies, reviewing building regulations and UK government net zero building guidance, the study aimed to identify design options that meet Passivhaus accreditation while remaining practical and market friendly. Using software Solutions such as Autodesk Revit Thermal Analysis and the Passive House Planning Package (PHPP), four design scenarios were analysed, each with varying building fabric insulation values and energy strategies.
Proposed Design Scenarios
Scenario A
Building Fabric U-Values were intentionally set as less efficient than those indicated in Approved Document Part L. This solution under the ‘traditional’ design intends to set out building strategies as they would have been conducted prior to an industry wide cognizance of Low Carbon Design.
As expected, the energy model calculated the heating requirements when incorporating all the criteria set out for this scenario with a peak heating load of 208,985W and a Heating Load Density of 62.76W/m2.
Our heating loads will be the driving factor as to which solution is selected in any design scenario, for Scenario A the intended heating supply for both space heating and domestic hot water usage is a traditional oil-fired boiler system.
Scenario B
Scenario B was set out using Approved Document Part L Compliant U-values to assess how much the building fabric can reduce the overall peak heating load – resulting in a peak heating load of 94,979 W and a Heating Load Density of 28.52 W/m2.
The main difference between the two scenarios A & B, is that the building fabric is better insulated, as indicated in the peak heating load of which there was a percentage decrease of 54%.
With such a significant reduction in mind, we can explore the option in Scenario B by pairing this lean heating load with an air source heat pump solution. Note that in this scenario we can see the Heating Load Density drop significantly too, this has been reduced to 28.52W/m2.
Scenario’s C & D
The requirements for Scenarios C and D are to be drawn from the PHPP (Passive House Planning Package). For both these scenarios Passivhaus complaint U-values have been determined.
For both Scenarios C and D, the required heating and heat losses will remain the same. The key difference between these two scenarios is the primary energy demand renewable offset being applied in Scenario D with the intent of achieving Passivhaus Premium.
Specific heat Losses, Gains and Heating demand – PHPP
It should be noted that the heating demand in previous scenarios was calculated on a W/m2 value, so to get a whole building per annum value the PHPP outputs shall be consulted.
There will be a potential for further reductions to the building cooling load if the student accommodation block is to be unoccupied in the summer months, a decision which is up to the client and their needs on campus during the months of June-September.
The PHPP Output is significantly more robust than the Revit energy modelling with heating and domestic hot water loads being split out. For comparison we will review the Space heating load only when comparing it with Scenarios A & B. We shall consider the domestic hot water load of the air source heat pump when assessing the Renewable Energy offset to be indicated in Scenario D.
PHPP includes the building orientation, daylighting and occupancy data to include values for winter and summer supplies as well as factoring in storage losses. Potential risk of storage losses will be more prevalent over Air Source Heat Pumps (ASHP) heating used for domestic hot water systems due to the nature of the ASHP operation. Any losses can be mitigated with additional immersion heating local to each storage cylinder.
From the PHPP it was determined that Space heating peak load to be supplied by ASHP was 56,423 kWh/a, Winter domestic hot water peak load supplied by HP was 38927kWh/a and Summer domestic hot water peak load supplied by ASHP 41124kWh/a – with all values accounting for storage losses.
With the above considered, we can check the PHPP passmark and review where any shortfalls may be to target the next step up on on the Passive House grading.
Scenario D
In Scenario D, the intention is to draw a proposal targeting Passivhaus Premium through renewable energy generation on site.
To satisfy the Passivhaus Premium requirement, it was calculated that 136kW of photovoltaics (PV) would be required. This would take the form of 400 No. 340W panels located in the adjacent field to the main project site.
With the above considered, the PHPP passmark proved that the proposals would achieve our target of Passivhaus Premium on the project.
It is evident that PV alongside a battery storage facility is a favorable solution when ensuring there is resilience with the power infrastructure of the project. Battery storage facilities and the associated installation methods have a higher capital cost than a direct supply PV array, however the benefits include resilience in usage of stored power on low daylight hours days, the opportunity to impot from the grid during low tariff hours to top up the battery, and the opportunity to store excess to sell back to the grid should such schemes become available in Northern Ireland.
The study concluded that Scenario D, which incorporated on-site solar PV generation and battery storage, was the only option that successfully achieved Passivhaus premium standards.
Economy
Economic analysis revealed that while low carbon building solutions and Passivhaus builds incur higher capital costs, they offer long-term savings in fuel consumption and improved tenant well-being. Further work includes examining potential site relocation and promoting renewable technologies not feasible in the current location.
Legislation & Government Support
Additionally, the study suggested that future government support through initiatives like smart export guarantees could enhance the economic viability of Passivhaus projects.
This research demonstrates the potential for Passivhaus standards to contribute to energy efficiency, carbon reduction, and improved thermal comfort in the new build student accommodation and residential markets.
This Technical Bulletin has been prepared by Nathan McGregor, BIM Manager, Bennett Freehill.
