[Equest-users] T-Stat is acting Screwy

[Rob Hudson]

I have not yet solved it.  My boss came over to me this morning and said we
are not to change the thermostat set points, so everything is as it was
prior.  This was a major ECM for the project, but i guess its gone now...
hehe
I think if i have more time i will attempt to take a crack at it again.  The
internal loads were minimal in the otherall design ( i think 1.4 w/sqft for
lighting and ~3 w/sqft for equip loads.)

On Fri, May 21, 2010 at 9:03 PM, Eric O'Neill
<elo at michaelsengineering.com>wrote:

>  Very interesting. It hadn’t occurred to me that you might bump into the
> dehumidification set-point during night setback (then again, a lot of things
> haven’t occurred to me). But it seems to need to be under a set of just
> right conditions. When could the space cool down fast enough at night, while
> still having a high enough humidity level to trigger dehumidification?
>
> I don’t think this would occur during the winter. Let’s assume this
> building is up north where shell losses can add up and cool a space down
> relatively fast during winter. Even if you’re humidifying to 40% at 70F
> during the day (which he’s not) and dropping to 60F at night, you’re only
> hitting 57% RH, assuming constant absolute humidity. For a lab, the make up
> air (which has a low absolute humidity because of the low ambient
> temperatures) would probably dry out the space before the indoor temp hits a
> point low enough to set of dehumidification.
>
> So the other possibility I see (which is what Fred described, I believe) is
> that during some nights the make up air is bringing in moist, cool air, and
> the system isn’t tempering it because the zone is satisfied. So this extra
> air cools down the space and drags up the RH, triggering a dehumidification
> mode that would be unnecessary at 70F indoor set-point. But if this was the
> case, wouldn’t your heating energy go down more than slightly due to the
> reduced ventilating loads?
>
> What am I missing here? How large are those internal latent loads (seems to
> be a wild card to me)? I’m curious as to whether you’ve solved this one Rob.
>
>
> Cheers,
>
> Eric
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Fred Porter
> *Sent:* Wednesday, May 19, 2010 7:07 PM
> *To:* Rob Hudson
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] T-Stat is acting Screwy
>
>
>
> Rob,
>
> I'm a little unclear about statements like "I looked at my SAT and it is
> controlled by a reset schedule." Does this mean that the reset schedule a)
> came from "The Wizard," b) actual AHU sequences, c) a departed modeler (you
> know who you are!) or some other source. This is important and should be
> checked.
>
>
>
> What's happening to increase the cooling coil load is that at certain hours
> the baseline reset SAT (e.g. 60F high RH) is not providing 53% RH indoor
> conditions at reduced 65F zone temp even though it did at 70F. So DOE-2.2
> resets down to the MIN-SUPPLY-T (probably 55F) in the "parametric" with the
> setback zone Ts. Thus, coil load shoots up at those hours, and there are no
> hours where the cooling load is decreased by changing, even increasing, the
> zone Ts.
>
>
>
> The lab users need to decide whether the appropriate upper RH limit is
> really 53%. It if can be increased, then you can save money by increasing
> it, and instituting setbacks. And perhaps a setpoint decrease to only 67-68F
> *might* give better results in reality and model land. But it sounds like
> you are unsure of some of the model and the lab requirements. If this is
> the case I would be very careful about making recommendations to lab owners
> and users along the lines of "....reduce zone heating setpoint to 60F,"
> because if they could just do that, they might not spend millions of dollars
> on Phoenix valves to control VAV. You need to model the correct SATs, and
> only reasonable zone conditions.
>
>
>
> Fred Porter
>
>
>
>
> >>> On 5/19/2010 at 1:21 PM, in message <
> AANLkTinV1_p5XWNJrIiRwocYPovZQVPlvHc1Uzu0DixR at mail.gmail.com>, Rob Hudson
> <rdh4176 at gmail.com> wrote:
>
> I'm trying to wrap my head around this the best i can.
>
> I looked at my SAT and it is controlled by a reset schedule. the
> temperature of the space never reaches anything above about 72 deg, which
> makes me think that what you are saying is very true and the heating t-stat
> schedule is in control all the time.
>
> So can you tell me what it is that i can do to fix this?
>
> On Wed, May 19, 2010 at 2:52 PM, Fred Porter <FPorter at archenergy.com>
> wrote:
>
> Rob,
>
> OK, I can't resist a bit of lunchtime "Stump the Chump." First I'd say
> verify the setpoint change in the runs is actually working by examining SS-O
> for the baseline and parametric run. But I'll assume it is, and offer my
> explanation.
>
> One piece that is left out in all this is the SAT control.... very
> important for a CV-reheat application. And LOCATION!
>
> My bet is that your SAT is resetting down at night based on hitting the
> upper RH limits during the setback scenario. This is why the CHW load
> increases. This is also why HW savings might not be as great as expected.
>
> Holding all else the same, the hourly temperature in a lab zone will with
> minimal internal gains as described will follow the heating setpoint down;
> the cooling setpoint will not be in control. Generally this will lead to
> high internal *relative* humidity (which is why this setback is only done
> carefully and to a limited extent in labs) from the OA for many hours, even
> if internal latent gains are nil. If the "baseline" model has any SAT reset,
> the MAX-HUMIDITY resets the hourly SAT back down to the MIN-SUPPLY-T when
> the model zone RH exceeds the RH setpoint, in this case a relatively low
> 53%. This increases in frequency as the zone temperature decreases.
>
> Fred Porter
>
>
> >>> On 5/19/2010 at 9:24 AM, in message <
> AANLkTinsmv-lXFuk3A65lvU2asMT_VshFXVOYiSk6xwB at mail.gmail.com>, Rob Hudson
> <rdh4176 at gmail.com> wrote:
>
> Thanks for your thoughts and here is your answers:
>
> 1) yes, but there is no night set back time.
> 2) everything is 100% oa and constant volume 24/7/365
> 3)no exhaust heat recovery, and steam preheat. the thermostat is set for 70
> - 73 heating and cooling and the set back is to 60 and 80 at night for my
> parametric run.
> 4) the cooling comes from a central chilled water plant for the entire
> campus, and i just created a chilled water loop, added a meter and a pump
> and it seems to be running happily.
> 5) the fans run all the time, day and night
> 6) I do have internal loads with latent heat, and it cycles down at night
> to almost nothing. These loads are currently the same for the model and the
> parametric run.
> 7) i have set humidity levels to 20% and 53%, which also do not change with
> my parametric run.
>
> hope this give you enough information.
>
> thanks again
>
> On Wed, May 19, 2010 at 11:13 AM, David Bastow <
> dbastow at mcclure-engineering.com> wrote:
>
> Rob,
>
> I have a number of questions:
>
>    1. Do you have many lab hoods? And are exhaust and make-up air revised
>    for the lab hoods at the night set back time?
>    2. What is the percent of outside air to the lab? Does this percentage
>    change during the night set back time?
>    3. Do you have a pre-heat or exhaust heat recovery and pre-cooling on
>    your make-up air? What is the temperature setting of this pre-heat or heat
>    recovery and pre-cooling? Does the temperature settings on these change at
>    the night set back time?
>    4. Do you utilize an air or water side economizer for 1st stage
>    cooling? Does this use change any at night set back time?
>    5. Does the fan run continuously day and night? Have you ran models
>    with the fan running continuously, and with fan cycling based on demand at
>    night and off completely at night, to see how the results compare?
>    6. Do you have a internal load watts per square foot and latent load on
>    the space from interior lighting and equipment? Do these loads change at the
>    night set back time?
>    7. Are you adding humidification or dehumidifying the space based on
>    some humidity settings? Does the humidity settings change during the night
>    set back time?
>
>  One of these things is probably causing the increased chilled water
> cooling load. Often if you have high internal loads, even at night, then
> changes to the fan cycling and the amount of outside air brought in at
> night, will increase the chilled water cooling load. I would review all of
> these areas and run various test models to see how they each affect your
> energy usage when modified.
>
> Our firm just completed modeling some very large lab facilities with more
> than 55 exhaust hoods in the building, with high internal loads 24/7 and
> 100% outside air. As long as the models are set up correctly they are
> normally right. It takes some real design and thermal dynamic thought and
> often may models to really get your mind right with what is truly going on
> with the facility. Its important to keep an open mind to what is going on.
> Having been doing computer hourly modeling for over 17 years, it is often
> easy to think you have a handle on what is going on with the building, but
> it is important to keep an open mind and investigate all the different
> avenues that you can think of until figure out what is going on. I have 99%
> of the time that I have blamed the screwy program having problems that I
> have found that I just didn't look at all the different angles enough.
>
> *David A. Bastow *
>
> *McClure Engineering, Inc. *
>
>
>  ------------------------------
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Rob Hudson
> *Sent:* Wednesday, May 19, 2010 7:46 AM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] T-Stat is acting Screwy
>
> I have a lab space that is kept between 73 and 70 degrees all year long.
> One of my parametric runs has the cooling and heating T-stat schedules
> changing to have night time setbacks to 80 and 60, respectively. When i use
> these, i get more energy spent overall. specifically, i have a chilled water
> meter, steam meter, electric meter and hot water meter to monitor
> everything. The chilled water increases while the others slightly decrease
> when i use the set back schedules. Any ideas?
>
> --
> Rob Hudson
>
>
>
>
> --
> Rob Hudson
>
>
>
>
> --
> Rob Hudson
>
>
>



-- 
Rob Hudson
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