[Equest-users] T-Stat is acting Screwy

[Carol Gardner]

Hi Rob,
You can send your .inp and .pd2 files to whoever you trust to look at this.
You are aware, of course, that we are all working: some for others some for
themselves. Someone will either give you the gift of a free peer review or
you can request one of us to do a peer review for a sum of money. Always
remember that you get what you pay for.
Regards,
Carol

On Wed, May 19, 2010 at 12:21 PM, 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. *
>>>  <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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-- 
Carol Gardner PE
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