I'm trying to set up a really simple 2 story building with 6 rooftop units. Two 60 tons supply cooling only to the core of the two floors and the 4 15 ton units take care of the perimeter. One unit supplies air to two walls on the first floor and another unit takes the other two walls on that floor. This is repeated on the second floor. In the wizard I set it up exactly like this and inputted the performance data for each unit and named each unit but when I go to detailed mode to modify the schedules to reflect the controls of the system it has broken everything out completely different than what I assumed I had set up in the wizard. I've attached the .pd2 file, I don't know if this is sufficient for anyone to look at what I've done.
I appreciate anyone help on this.
[outlook sig]
Hi Travis,
You need to attach the .inp file that this .pd2 file uses, too.
Carol
Thanks
Travis Rhodes
Hey Travis,
What you've currently got is:
- A 60ton unit for each floor's core zone (2 total)
- A series of 5 and 7.5 ton units each serving one perimeter zone (8 total) ? note: cooling capacities appear to have been edited after the wizards
- Total units: 10
- Picture:
It sounds like the desired is to have:
- A 60ton unit for each floor's core zone (2 total)
- 15 ton units each serving two perimeter zones (4 total)
- Total units: 6
To pull this off you need to
1. Go back to wizards
2. Review/Correct the tonnage for the smaller units, as necessary (wizard inputs don't reflect 15 tons all around)
3. Select "system per site" in the first screen of each system (note: you've got "system per zone" selected currently, which assigns one system of the specified sort to each zone in the shell associated... this is the main source of your system quantity issue).
4. Assign the perimeter zones to the appropriate systems (looks like you've already done this correctly, but review to be sure assignments are correct).
When finished and on exiting the DD wizard, you should observe the correct quantity of systems and zone assignments on review of the airside HVAC tab/component tree.
Best of luck!
~Nick
NICK CATON, E.I.T.
Why not just do it detailed edit? It's pretty easy to do there so I'm
wondering if you have a reason I am not thinking about for going back into
the wizards.
Carol
The reason is because I've never used eQuest before and figured I'd start with the wizard to see how far I would get.
Nick, thanks for the help, I'll see how far I can get now. :)
Travis Rhodes
I apologize for these soft ball questions in advance, but I'm very appreciative of the help. If one of the 60 ton package units supplies 20 VAV boxes, do I need to model 20 zones with the 60 ton as the parent unit to these zones, or can I tell eQuest somewhere that there are 20 VAV boxes with 20 thermostats in one single zone?
Travis Rhodes
Travis,
To this latest question - you can go either way. Modeling a separate zone for each VAV is more accurate and permits specifying varying capacities/loads/scheduling within the spaces. I perceive this as a necessary degree of accuracy for something like a LEED submittal. Calling it one zone means you're modeling one monster VAV which will approximate all 20 VAV's in combination, operating in sync. The capacities (heating/cooling/airflow) will autosize large enough to handle all zones at once and you'd specify "representative" efficiencies/scheduling/fan kw/cfm and so forth to roughly equate to a "typical" unit. This level of accuracy is what I'd call normal/fine for modeling to compare various HVAC systems to approximate relative changes to other elements like LPD or setback scheduling. What level of accuracy you "need" is entirely up to the modeler (and reviewer, if applicable).
Regarding Carol's response earlier:
Carol is quite right and raises a point I forgot to mention - the issues below are entirely "fixable" within detailed mode (as with most things). I took an approach to outline "what went wrong" in wizard mode however as it was apparent Travis had a clear goal and simply missed something along the way, after seemingly doing everything else right.
I fully agree with Carol that these particular issues are just as quick (if not quicker) to resolve in detailed mode. In my humble opinion though, taking a few minutes to learn how to use the wizards correctly is worth the extra effort as you won't be making the same mistakes to fix in your next models =). To be clear, there's nothing in the wizards you can't do in detailed mode - the only compelling reason to "go back" to wizards is if you (1) have nothing/little to lose (you haven't done much work in detailed mode) or (2) you feel the time saved making a change in the wizards will outweigh the time lost re-doing the detailed mode work (like when your zone map has completely changed up).
I prescribe to the following mantra: "Use the wizards to their fullest time-saving extent prior to entering detailed mode." Another way to put is "do as much as you can that you can't do faster in detailed mode." This is obviously a moving target that varies project-by-project and with one's experience level, but it's what I strive for and this philosophy illustrates that the question of when to get out of the wizards never has a black and white answer.
Some prefer to get out of wizards ASAP because they're very fast/comfortable with detailed edits, while others spend time wrestling with the wizards far longer than they should to achieve things that are done more quickly/easily in detailed mode. I was solidly in the latter camp when first learning eQuest and feeling apprehensive about detailed mode, and I know others have the same hurdle... but in time everyone strikes a personal balance and preference - you really figure this stuff out with experience and trying new things. I'm self-taught for the most part, but learning what is most efficiently done before/after the wizards is an area of knowledge I would expect to be covered in quality formal training at various levels, as this is the sort of topic that otherwise requires "doing it wrong once" to really learn.
I'll be out of the office thru the rest of this week, but Travis if you or anyone else is interested in how to accomplish the same edits in detailed mode and can't figure it out, simply ask! I'm sure Carol and others would be willing to help as individual time allows ;).
Happy to help and best of luck!
~Nick
NICK CATON, E.I.T.
Thanks, Nick. Good explanation. I agree with the use the Wizards to their
fullest capability method, and that it's a moving target based mostly on the
modeler's experience. For me, I have run into stability issues in the
Wizards, e.g. screens freezing, files crashing, enough that I just don't
trust them. I get out quickly.
Carol
All: Following is an off-list question/response I felt others could benefit from in a general sense. Posting to the list with Jonathan's assent =).
Hey Jonathan,
To be clear, I was careful to phrase that's just my feeling/sense for a "LEED-level" project. So many things are subjective when it comes to LEED reviews, and what may be a "fine" assumption for one project may be a "gross over-estimation" to another reviewer... don't get too caught up!
As a general rule, in the world of energy modeling, I'd say any decision with sound reasoning behind it is a "right" decision, and oftentimes (esp. outside of structured systems like LEED) that's the only guidance you'll find. As long as you personally can explain/reconstruct the logic behind your decisions, your model is just as accurate as it has to be! I personally like zoning my models in a way that matches actual terminal unit zoning because it means I can follow the scheduled capacities/loads to the letter when doing checks or being asked to quantify/verify whether the loads are in the same ballpark. I'm personally (again, not prescribing anything here) likely to simplify the zoning heavily whenever the purpose of the model is to explore the effects of things that aren't sensitive to terminal unit quantities.
I do not and would not argue your decision to zone differently than I would is "wrong." I'd rather defend that you're in the best position to make that particular decision ;). The responsibility/onus of the modeler to make this call is generally supported in the 90.1 User's manual, should you ever require more than a fellow modeler's opinion, by the way!
Best of luck!
~Nick
NICK CATON, E.I.T.