Hi all,
I have a Gas INFRA-RED radiant heater in a big space. I tried to model it as a unit heater, heat source=furnace, enter heating capacity same as my mechanical sch.
Under SA-V report shows a lot of CFM for fan that is wrong in my case, because there is no supply fan.
How can I fix this in my propose and baseline plan.
Thank you,
Arash Pasgar
I would model the radiant heater as baseboard and set you supply fan in the proposed to something low like 10 CFM and put in 0 for the supply fan power. Also if this space is not cooled, I would use a thermostat schedule for cooling that is high enough that the cooling never turns on.
In the baseline remove the baseboard. Let the CFM autosize and set the fan power to the allowable kW/cfm as specified in Appendix G.
Tim.
Timothy Howe, MS, LEED? AP BD+C
Thank you Tim.
To make it more clear. I have a 2500 sf shop without any cooling and just gas infra-red radiant for heating.
I think I have no other choice to select unit heater for proposed plan an just over ride the cfm to 10 as you said and enter the heating capacity.
I think I need to do exactly the same for baseline. Am I correct?
Thank you,
Arash Pasgar
Technically you need to model both heating and cooling in the baseline and proposed.
You can work around this technicality by modeling the zone thermostat as I stated. Go crazy set it to 999 in the schedule, but make sure you set the Indoor Design Temperature to a reasonable value or things will go sideways in the autosizing of your system capacities.
In summary,
Baseline: Model it as a packaged single zone system. Autosize the CFM, fan power based upon Appendix G requirements, cooling (1.15 sizing ratio) and heating (1.25 sizing ratio) capacities, cooling and heating unitary power based upon capacity and 90.1 min efficiency values.
Proposed: Model it as a packaged single zone system. CFM = 10, kW/CFM = 0, cooling (1.15 sizing ratio) and heating autosized (1.0 sizing ratio), but put the radiant heater in the baseboard inputs (I would do it this way so that it does not rely on the air side (the 10 cfm) to convey the heat to the space.. Not going to work). Cooling unitary power same as baseline and proposed based upon the radiant heater eff
Thermostats the same in both cases.
Tim.
Timothy Howe, MS, LEED? AP BD+C
"Technically you need to model both heating and cooling in the baseline and
proposed"
... only for LEED models.
You can also model a different HVAC system that includes cooling (and
allows for a baseline), and simply set the cooling capacity to 0.
--
Karen
Karen,
Unfortunately that does not work. Setting the capacity to zero will just make the program autosize it for you. The only way to prevent the cooling from activating is through the thermostat setting.
Tim.
Timothy Howe, MS, LEED? AP BD+C
... so set it to 1
That creates unmet load hours.
Timothy Howe, MS, LEED? AP BD+C
As you said, on my proposed plan for infra-red I model it as a baseboard (furnace).
On baseline plan for that space I select single package zone. My problem is, how to model gas consumption.
Right now my saving is -102 for gas.
Thank you,
Arash Pasgar
I attached the files.
Arash Pasgar
All,
To play devil's advocate: If you feel a LEED reviewer would approve of modeling a cooling system that simply doesn't do anything, what about simply not define a cooling thermostat schedule? Makes capacity and unmet hours both non-issues and the thing will never expend energies trying to cool. As always, baseline thermostat schedules (or lack thereof) should match the proposed.
That said, I'm going to stir the pot and say I'm not advocating this approach. My reading of 90.1, independent of LEED reviewer commentary, is we're supposed to actually heat and cool all conditioned spaces in the proposed design, even if only heating or cooling is provided. Providing cooling or heating means in the system set up to never cool or heat misses the point*. I have not tried addressing the issue in that fashion under a LEED review (on the contrary, I cooled the space in a baseline-equivalent fashion). I can only caution a reviewer may not agree with the less conservative interpretation - if others have experienced otherwise, please share!
~Nick
*PS: Honestly I can only speculate, but I think the "point" of this rule is to not permit an 'unfair' advantage for buildings which do not require heating or cooling for a given area, relative to other buildings going through the performance rating method. If that's truly the goal, I personally think it would be more elegant to simply have the baseline follow the proposed design's conditioning requirements. As it stands, it sort of "punishes" building owners/designers for saving energy by recognizing designed conditions of comfort can and should vary by space function.
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
That's a well stated approach John, and one I'll probably make use of - thanks for sharing!
The anecdote you heard about someone slapping on a cooling unit after the plaque is kinda disheartening, but I have to concede makes sense. I'm stuck for an improved solution that addresses that problem without becoming a real headache for the modeler/reviewer. In a positive light, I suppose the present annoyance isn't nearly as bad as a hypothetical team intentionally planning on using the model as a means of deception like that.
~Nick
NICK CATON, P.E.
Having heating and cooling has been a requirement of ASHRAE 90.1 staring with Section 11 in 1999(as far back as I can go) and in both Appendix G and Section 11 in subsequent versions. LEED only comes into play because it requires the following of the Appendix G.
Also note that addendum to 90.1-2007 has revised the requirement of having cooling in a heating only system which will not have cooling installed in the proposed design. You are then allowed to model heating only in both baseline and proposed of course.
I tend only to use the thermostat method judiciously when there is a heating system only, the fan power is dramatically less than the baseline allowance (unit heaters or radiation only) and will create an unfair advantage for the proposed system.
Now to have a kW/CFM input for heating and cooling would be great and remove this issue completely.
Tim.
Timothy Howe, MS, LEED? AP BD+C
Our job as modelers is not to get as many LEED points as possible; our job
is to model the building and the baseline as accurately as possible. There
have been times when I've had to tell clients that their "super-efficient"
building does not meet baseline LEED requirements. It's not an easy
conversation, but if you're polite, informative and help them reach resolve
the issue, it's not so bad.
John's method respects both the requirements and the building design, but
blanket advocacy of the "thermostat method" does not.
--
Karen
Is there a place in the documentation that details how eQuest calculates
supply airflows? I'm modeling a VAVS system, and it seems the
MIN-SUPPLY-T for cooling and MAX-SUPPLY-T for heating are used to arrive
at cooling and heating CFMs, and the larger of the two is applied as the
airflow to that space (plus OSA I'd imagine).
I have a space that has a cooling load of 108kBTUh and a heating load of
-36kBTUh. I've done a handcalc (Q=1.8*cfm*deltaT) to arrive at the
following:
Cooling: (supply at 55, space temp at 75) -->3000cfm
Heating: (supply at 95, space temp at 72) -->870 cfm
OSA requirement is 4200cfm.
By hand, I calculate a value of around 7200cfm. However the value listed
as supply flow in the SV-A is 71225cfm, about an order of magnitude
larger than what my hand calc suggests.
Am I thinking about something incorrectly here, or can anyone point me
in the direction to find documentation on how eQuest calculates airflows
so I can try and troubleshoot the inputs that would affect the answer?
Thanks,
Erik
Erik,
You can download the DOE-2 Engineers Manual here:
"DOE-2.1A Engineers Manual (theory and algorithms of calculation for the original DOE-2 program - out-of-date but most of the concepts are still used in DOE-2.2 - LOADS calculation is very similar, air-side HVAC is similar but improved, water-side HVAC is completely new but has some similar approaches):"
http://doe2.com/download/DOE-21E/DOE-2EngineersManualVersion2.1A.pdf
Where are you getting the loads from? If it is from DOE-2 LOADS reports, I don't believe any of them account for ventilation, only infiltration. You have a large ventilation load.
Be sure to use 1.08, not 1.8, in your handcalc equation.
You could share your model files with the forum, and/or compare your results to the actual design if it exists.
Regards,
Bill
Hi,
You don't need to add Outside air to supply air flow .
Supply air flow= outside air+ return air
But your outside air is more than supply air flow ( I hope this calculation
you check).
Uday.....