Sim List,
I'm simulating a LEED DES model of a campus central steam plant.
Under the new requirements discussed below specifically addressing 'step
1'. The way that I read the document, step 1 requires that the "upstream
equipment [be] modeled as COST neutral" (Table 1, p.4) while the
baseline DES system is compared with a proposed system "As Designed"
(Table 3, p.6) which suggests that the upstream DES equipment (including
its inefficiencies) shall be modeled in the proposed building for step
1.
If I am reading this correctly, it would be much more difficult
to acquire the required 2 points for certification (14% - NC) than
previously suggested.
Also, the comparison for systems not directly affected by the
DES central plant (chiller in my case) is not necessarily a direct
comparison. My building is ~75,000 SF & 3 floors (fossil fuel /
purchased heat), therefore according to Table G3.1.1A & B my baseline is
system 5 Packaged VAV w/Reheat - cooling type: direct expansion.
Any and all thoughts on this topic are welcome
Thanks
Eric
Thanks Paul,
I guess I was just stating that the comparisons on equipment are
not so direct when you have one source from a DES system. Also, I'm not
really sure if I'm interpreting correctly that the DES being modeled in
the proposed but not in the baseline is fitting the intent of holding
the upstream equipment cost neutral. I suppose that it is as long as the
heating source is separately metered and the rate applied is the same.
Thanks,
Eric
Dear Eric,
The Proposed system savings is built up from
* better wall and window constructions (resulting in smaller loads)
* better lighting design (resulting in smaller loads)
* more efficient equipment for HVAC
* operated with greater sophistication
When you put all of those together, 14+% is not so hard to achieve (even if
your DES is not state of the art)
James V. Dirkes II, P.E., LEED AP
David,
My question relates to step 1 only. My is that step 1 is not
requiring identical purchased heat for both cases. It in fact states
that the Proposed building should modeled "As Designed" while the
Baseline building is per Appx G except for heating type energy source
(Table 3, p.6).
I'm not sure if I'm interpreting this correctly. It seems, as
you stated in the previous reply, that the intent is to hold heating
energy neutral, but the way it is stated is 'COST neutral'--not energy
neutral (Table 1, p.4 - EAc1, Step 1).
Eric
I am also in the middle of a DES project at the moment. The way that I
interpreted Step 1 and 2 is as follows:
Step 1:
Baseline: all downstream (on-site) equipment, envelope components, etc, as
in Appendix G. heating and cooling is purchased from a DES system.
Proposed: all downstream (on-site) equipment, envelope components, etc, as
designed. Heating and cooling is purchased from a DES system.
Step 2:
Baseline: all equipment is modeled as on-site. Boilers and Chillers are to
be modeled as designed in Appendix G. Utility rates are to be local utility
rates
Proposed: building is to be modeled as built. Heating and cooling is
purchased from a DES system, energy costs must take into account DES
production and transmission losses.
In my opinion, the vocabulary in Table 1 is confusing, but the guidelines on
pages 5 and 6 seem pretty clear. Am I on the same page as everyone else
here?
Thanks,
--
Karen
Eric, David & Karen,
Thank you so much for discussing this document! It needs it.
I agree Karen & David through step 1.
But as I read Step 2, the proposed model must include analysis of the DES plant in such a way as to show the conversion from loads at the building to corresponding fuel consumption at the DES plant to corresponding dollars. If you could stop at the dollars per load charged to the building, why did the anonymous authors provide default efficiencies and losses on page 8.
That is not to say that I agree with how the document is written. I still have the following issues:
- does the document imply all baseline DES cooling systems are electric?
- does the document imply all baseline DES heating systems are natural gas?
- whose rates are applied to the DES energy consumption? The building's or the DES's?
The document anticipates refinement and invites correspondence to leedinfo at usgbc.org.
Has anyone submitted a Step 2 model to the USBGC and received feedback or approval? If so, please share.
Paul Riemer
Karen & David,
Thank you for your input on this topic. I tend to agree
with both of you about the intent but I would have a hard time pointing
to any specific text if anyone were to disagree with this
interpretation. The wording is a bit unclear. Pages 5 & 6 seem to simply
refer back to tables 2 & 3.
Good luck with your project Karen...
Eric
Sorry, correction to my earlier post -- for Step 2 it should be a virtual DES, regardless of if you have a tariff to use or not. The virtual plant would be consuming equivalent fuels to produce the DES services.
David
I just finished my first DES project (not submitted yet, though)?and have a couple more in the works.??
I agree with the interpretations below especially with respect to Step 2 and the utilization of the DES purchased rates?as an acceptable means of reflecting the prposed/actual central plant's efficiency in the proposed energy model.??Although, the DES purchased rates should reflect/be adjusted?for the?items Karen mentions.? Additionally,?I'd recommend confirming that the?DES rate includes all the?central plant's bits and pieces.??The maintenance costs should also be extracted from the DES rate if possible.? (The DES document seems?to clarify that the maintenance costs do not need to be included.? So, if those can be extracted that will be more of an apples to apples comparison with the baseline model and work in your proposed model's favor).?
In my estimation, the above method provides the most expedient, realistic?and accurate method of determining the central plant's efficiency.? The trick is that that info is not always available - especially in a campus situation.? So, in that case you may need to use one of the other methods of modeling the central plant discussed in the DES document: other metering data, modeling of the central plant equipment, etc.? However,?sometimes even this data can?be hard to come by and/or is not within the project's ability or budget to determine or model.? So, in that type of situation, the?default central plant efficiency values provided in the DES document could be used.?
Julia,
Thank you for your comments. Please allow me to ask a bit more.
Are you stating that Table 1.8.2(b) at the bottom of your Step 2 EAc1 template will have an energy type line item of "hot water", "steam", or "chilled water"? If so, will the numeric energy use value (e.g. 1,234 MBtu) be exactly the same as in Step 1's EAc1 template? Meaning the only differences between the proposed columns of the two submittal templates will be the dollar costs of the DES energy stream and total costs?
Paul Riemer
Let me reiterate, that?I have not submitted my model yet to LEED.? So, I don't have any feedback from them regarding the?validity of my take on things.
In aswer to your question: Yes and no. :)
The way I see things:
For?Step 1, the DES document talks about using a "market" rate for the DES utilities.? So, my take on that is that if there is a general prevailing rate for these utilities in your area, that should be used in Step 1.? Where as the intent for Step 2?seems to be to use info (i.e. a rate or other method as discussed below) that reflects your plant's actual efficiency.?
In theory, for Step 1, the rate shouldn't matter since?it's effect is neutralized by using it in both the proposed and baseline models.? However, I'm thinking there may be a situation where if you have a really?stellar?(i.e. low CHW, steam, HW rate) or poor (i.e. high CHW, steam, or HW rate) performing proposed central plant and you use that rate in Step 1 in both the proposed and baseline models, it may impact your results in Step 1.??Although, again, in theory, it shouldn't matter.? But, as I do more?models,?it seems that the?relationship between $ saved and the % saved is not?linear - i.e.?as you demonstrate more and more savings, it seems easier to get to the next LEED increment with smaller amounts of deltas -?and vice versa?(which to some degree makes sense since dividing by smaller numbers).??But, I'm thinking?this effect could impact your savings in Step 1 and thus your ability to even get to Step 2.? But, maybe I'm off base
here.? I'm speculating at this point in that regard.
That being said, it does seem?that the rate you used in Step 1 could be the same rate used in Step 2 for your proposed building and thus, the performance shown?for the proposed building models on the LEED templates?could be the same in both Steps.?
Another idea??I had was that the?DES rate could be used to back calculate the overall COP/efficiency of your plant.? And then use those figures in your proposed model for Step 2.? It may be easier to adjust those rates for distribution losses etc.? All this assumes that your DES rate is based on metered data?and actual production costs.? It seems LEED?may want some demonstration of this.??
?
Julia,
I have been a bit up in arms about how this document will apply to some of the DESs serving our client community who are perhaps a bit unique in doing things like:
- billing buildings only on peak demand (not consumption)
- generating chilled water from waste heat outside of CHP situation
- generating heat by burning some rather cheap things including garbage
(if they get paid to take it and burn it, probably best to just count it as free and not press the luck on a negative fuel cost)
I have been assuming that the Step 2 template would have to include the proposed DES energy consumption documented in primary sources like electricity and natural gas and the corresponding costs extended from those specific consumption numbers. That could get pretty complicated for some of the above scenarios.
Your tact looks considerably simpler and could remain abstracted above my questions about detailed fuel sources and detailed utility rates.
Thank you all for your comments so far and please do share if you have a Step 2 approach reviewed.
Paul Riemer
Dear List folk,
I recall a post that might have occurred about two - four months ago, in
which someone mentioned a film or membrane that was applied to the pitched
portion of an attic roof. The film had radiation blocking properties or
something like that (I wasn't interested at the time).
If my memory is correct, will someone point me toward that post or a source
which describes that product?
Thanks in advance.
James V. Dirkes II, P.E., LEED AP
Hi Paul,
Hmmm.? Those situations do?sound complex and tricky.? I've only had to deal "plain vanilla" central plants at this point.?
My thought/comment would be that it seems valid to use a simple cost for the chw or hw ($/therm etc.) in the DES step 2 models in lieu of modeling?a central plant?IF???that cost is?truly reflective of the central plant's efficiency.
In the cases you describe below, it sounds like there may be a disconnect between cost and efficiency.? Sounds like you would need to?model a central plant in?Step 2 that is reflective of the central plants efficiency.? You could?ignore any unusual methods (burnt trash?etc) in the model.??Then?you could?calc the dollar savings by hand afterward and deduct that?via the exceptional calc or renewable energy savings on the EA cr 1 template.? This seems like it would meet?the requirement to reflect the actual efficiency of?your central plant but still give you credit for the dollar savings?associated with burnt trash or other energy saving or renewable measures.
Before you go through a lot of work though, it may be worth your time?doing a CIR or calling LEED to determine an acceptable approach.