Equest Users:
In my school model, I have added the Heat Recovery option to my VAVS system in the current model, and it throws results clear out of line, increasing electric power usage almost 3 times, with increased ventilation fan operation and space cooling year round, which shouldn't be necessary in Wyoming.
Looking for methods to modify input and correct these obviously errant results. There has been some discussion here earlier this week, tried a couple of the suggestions, without acceptable results. If adding another system to handle the heat recovery or adding smaller heat recover to each zone is the right answer, please share the method for creating the new system in detailed edit mode.
Thank you in advance for your time and suggestions.
GINNIE SCHOFIELD
Adding correct .inp file for my question
Ginnie
Hi Ginnie,
IAQ costs money and bringing in fresh outside air to improve it is the
solution. Heat recovery depending on your climate doesn't always save
money but typically if you have hot humid summers or cold winters it
will. I would first take a look at your ERV/HRV schedule to make sure
it isn't running 24/7. You should also check it's relationship with the
economizers. It should be off and bypassed when they are running. You
only need fresh air for people when they are there occupying the building.
Bruce Easterbrook P.Eng.
Ginnie,
Higher fan energy and cooling energy are typical results when adding heat recovery.
Consider the following changes:
* The default 1.5" static on both sides of the HRV adds a lot of fan energy. You need to determine if this is reasonable and whether or not you should adjust the system fan power/static.
* ERV-RUN-CTRL is set to "When minimum OA". You are not simulating an economizer because OA-CONTROL is "Fixed Fraction". Therefore, you are always running the OA through heat recovery when the system is running, adding fan energy and cooling energy. Determine how the actual design will be controlled. OA temperature or OA enthalpy are typical.
* ERV-OA-FLOW is entered as 86,000 cfm, but the SV-A report shows only ~30,000 cfm OA. So you added a huge amount of OA when you added the HRV, which is probably not what you intended, and which contributed to the energy penalty.
Unrelated observations:
* Your plug load energy is low - only 1/10th your lighting energy. This is unusual and probably not reasonable. (They are nearly equal in most of my models.)
* Your ground floor surfaces are modeled as exterior surfaces, rather than underground. This will most likely increase your cooling load in the cooling months and skew the envelope loads the rest of the year. (I'm assuming the school is slab-on-grade.)
Regards,
Bill
William Bishop, PE, BEMP, BEAP, LEED AP
Bruce & Users:
Since an ERV/HRV schedule was not created with system, I tried to create one. That didn't work out so well for me. I believe my results are being calculated on 24/7 operation and NOT bypassed or off when running. Getting a proper operation schedule should help with the additional cooling shown on simulation reports. Any ideas or methods to create a schedule that will work?
Again, thank you all in advance.
GINNIE SCHOFIELD
Hi Ginnie,
I believe this needs to be an ON/OFF schedule.
Also take note of this help entry snippet:
ERV-SCHEDULE specifies that the ERV has its own operating schedule. Note that this schedule can lock out the ERV when it would otherwise be running, but cannot force the ERV to run when the HVAC fans are off.
Choosing "when minimum-OA" means the program won't use any schedule you've defined, you'll need to select the scheduling option in the same dropdown, then select your custom schedule.
Finally, be sure to take note of Bill's reply/advice (attached): Selecting "when minimum-OA," while not defining an economizer function (fixed fraction), means in net effect you are telling the heat recovery to operate at all hours the system fans are running. This can definitely be counter-productive, adding building heat into your airstream when you don't want to, increasing cooling energies, and so forth.
Regards,
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
Gentlemen:
Thank you for your input into my problem.
I have followed up on recommendations, and got an ERV schedule to work.
My new question comes back to selecting "when minimum-OA". . . . . . . . when I change the economizer function to OA Temp,
I still get increased cooling energies.
Thought maybe I could change my minOSA schedule from fixed fraction to temperature, and that didn't help the increased cooling energies.
Again, I do appreciate the assistance and recommendations from this users group, your help has proved very valuable in my limited Equest knowledge.
Ginnie