Hi everyone
We are trying to make some strategic decisions and would be happy about some feedback. First a short summary, two questions are below.
Situation is an existing office building with moderate renovations (C+S), some key points:
- nearly everywhere curtainwall facade, U-value facade around 2.4 W/(m²K) -> the facade is in good condition and will not be renovated, apart from some solar shading that must be redone
- roofs will be renovated and insulated
- cooling was provided through air with inefficient chillers -> after renovation, there will be cooled ceilings and purchased chilled water, air volume based on hygienic requirements
- heating is and remains purchased heat with radiators and floor heating
- lighting is replaced everywhere by LED
Using v4:
- The building envelope of the baseline building would be the same as the existing building, prior to renovations. As the envelope barely changes, this will provided hardly any energy savings.
- DES:
- Path 1: both baseline and proposed modelled with purchased heat and chilled water, only downstream equipment, identical utility rates, efficiency 100 % -> no energy savings
- Path 2: Baseline per Appendix G (efficiency 80%), DES virtual plant (efficiency maybe 85 %)
- Evaluation: comparison of energy costs -> depending on DES modelling path, but we don't expect high energy cost savings.
Using v4.1:
- The building envelope of the baseline building would be based on App. G in ASHRAE 90.1-2016 (Table G3.4-4), which would result in moderate savings in heating and cooling energy.
- DES:
- Evaluation:
Question 1: would you recommend v4 or v4.1 for this project? It is rather limited information, feel free to ask follow-up questions.
Question 2: Is it correct, regarding DES modelling, that path 1 does not allow to take credit for GHG savings?
Thank you for your time!
Sarah
Tyler Thumma
7GroupLEEDuser Expert
66 thumbs up
February 17, 2022 - 12:20 pm
1) Without modeling both scenarios it is difficult to evaluate whether v4 or v4.1 will be more beneficial, as it can change from building-to-building and location-to-location due to the combination of energy cost and GHG savings in v4.1.
2) It depends what you mean by GHG savings. GHG emission factors for each energy source must always be identical between the Baseline and Proposed building models, so in that sense you never get credit for GHG savings. However, for path 1 you would still apply GHG emission factors to the purchased heat and chilled water as well as electricity, and calculate the PCI, PCIt, and percentage improvement to determine the GHG emissions points in Table 2 of the credit language.
Hope that helps!
Sarah Leenknegt
Dr.Lemon Consult AG
4 thumbs up
February 23, 2022 - 6:13 am
Hi Tyler
Thanks for answering! We decided to try v4.1. Follow-up questions:
Question 1: DES, path 1, GHG savings in v4.1:
In Path 1, both proposed and baseline building would use the same DES-systems for heating and cooling, identical efficiency rates, identical distribution losses, identical energy sources, and identical GHG emissions per energy source. The savings potential is than purely building based, i.e. a (hopefully) lower energy use in the proposed as in the baseline building. -> correct?
- Question 2: DES, path 2, Proposed model
Full accounting of the DES performance, based on modeling and engineering data (no monitoring available yet, the DES plant is new). Am I correct, that we don't have to model the DES plant directly. Instead, we model a virtual DES plant. The implemented efficiencies etc. must be fully documented in the report, based on engineering data. If, for example, distribution losses cannot be determined analytically at this time, we can use default distribution losses as listed in the reference guide?
GHG emission rates based on the mixture of waste incineration and natural gas (heating) and electricity (cooling), as used in our DES plant.
If the DES plant uses a "greener" electricity mixture, do I have to use the same mixture for the baseline building?
- Question 3: DES, path 2, GHG savings in v4.1, Baseline model
Aaccording to the reference guide, we ignore the instructions of G3.1.1.3.3, to substitute the heating and cooling types in the baseline by purchased heat and chilled water. Instead, we model the baseline with the systems according to Tables G3.1.1-3 and G3.1.1-4, using the same energy source as in the DES system for the proposed. -> correct?
Our DES System (proposed) is:
- purchased heat: 80 % waste incineration plant, 20 % natural gas -> can I use fossil fuel boiler with natural gas as heating energy source in the baseline building?
- purchased chilled water: groundwater heat pump -> electric chiller as cooling source in the baseline building -> correct?
Thanks for your feedback!
Sarah
Tyler Thumma
7GroupLEEDuser Expert
66 thumbs up
March 3, 2022 - 10:57 am
Question 1: Yes, this is correct
Question 2: Yes, you model a virtual DES plant sized for the building only, and you do not need to model the actual DES plant if you're determining efficiencies based on an engineering analysis. You can use the default distribution losses from the reference guide when actual values are unknown. The emissions factors must be identical between the Baseline and Proposed, so you cannot get credit for a "greener" mixture. The only scenarios that would allow emissions factors to vary between the Baseline and Proposed models is if you're using hourly emissions profiles and limiting electricity demand during those times with high emissions, or using Tier 1 or Tier 2 renewable energy.
Question 3: Correct, you model the Baseline using the systems from Appendix G with the same energy source. For heating, the Baseline heating source would use the same mix as the DES plant (80 % waste incineration plant, 20 % natural gas). For cooling, the Baseline would use electricity in the form of DX or chiller(s) depending on the Appendix G system type.
Sarah Leenknegt
Dr.Lemon Consult AG
4 thumbs up
March 8, 2022 - 6:04 am
Hi Tyler
Thanks again for your feedback!
I am confused with regards to question 3. We are in climate zone 5A, and following Table G3.1.1-3 and G3.1.1-4, we should model System 7, which includes a hot water fossil fuel boiler.
In the reference guide (page 119) it says: "Baseline fossil fuel systems should always be modeled using natural gas, or propane in locations where natural gas is not available. Previous versions of Appendix G required the fuel type to be the same in the Baseline and Proposed case."
How else can we claim credit for the reduced GHG-emissions? If the energy sources in the Baseline must be the same as in the DES, then what is the point of including the GHG reduction points in v4.1? I understand your example in Question 2, but it seems a very special and rather theoretical case.
Best regards
Sarah
Tyler Thumma
7GroupLEEDuser Expert
66 thumbs up
March 8, 2022 - 8:44 am
Sarah,
The v4.1 reference guide does not include the same level of detail regarding the DES paths, so I was basing my guidance on the language from the v4 guide:
"All DES energy rates must be identical in both the baseline and the proposed cases. Use local rates as they would normally apply to the building for the energy sources under consideration. For energy sources used by the DES but not normally available to the building, such as diesel fuel, use the rates charged to the DES."
"Model the baseline building plant with conventional equipment using performance parameters and efficiencies per ASHRAE 90.1–2010, using energy sources corresponding to the DES."
The v4.1 reference guide says to contact USGBC to discuss the applicable modeling approach if claiming credit for an upstream district energy system, so that would probably be the best approach in this case. It's certainly possible that the applicable modeling approach will be identical to v4.
The purpose of including the GHG metric in v4.1, at least in part, is to encourage decision-making with respect to emissions and not just cost. For example, considering the emissions factors of a project's electric grid relative to other fuel sources and shifting energy use to the cleaner sources compared to a Baseline that is pre-defined regardless of the relative emissions of energy sources. Hopefully that makes sense.