[Equest-users] T-Stat is acting Screwy

[Rob Hudson]

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. *
>>  <http://www.mcclure-engineering.com/>
>>
>>  ------------------------------
>> *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
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