[Equest-users] BEST PRACTICES: Wild Coils

Fri Jun 21 13:16:31 PDT 2019

Nick,

Small world, I seem to run into this a lot too.

As for the eQuest side, I'll throw in a futile effort that I tried.  It's
been a few years since I've tried, so it may be worth another shot with
2.3, and also I may have been doing something wrong.  Under the coil
options, there is a CHW-Coil-Cap-fFluidFlow.  The default looks something
like this.

[image: image.png]

DOE2 uses this curve to control the cooling valve to modulate its hourly
output to meet a setpoint.  In other words, if I need X Btu/hr of chilled
water to get Y Deg-F air off the coil, how much water flow is that?  My
thought was to trick DOE2 with a custom curve which has almost zero
capacity except near 100% flow.  This would make the controller run nearly
100% flow through the coil regardless of load.  This curve would be like
the blue one below.

[image: image.png]

You are limited to cubic, quadratic, or linear profiles with this curve, so
creating this shape can be a little tricky.  This should force the valve
into nearly 100% flow all the time, but it won't model any space
temperature effects.

To try to model space temperature effects of a stuck valve that isn't
modulating, I've tried to create a curve with near constant capacity like
the green one below.  It needs to be slightly linear, or else you will put
the program into a death spiral.

[image: image.png]

In theory, this coil should put out near constant cooling output regardless
of the "flow" that DOE2 puts through it.  Again, last time I went down this
rabbit hole, I was unsuccessful, but it may be worth another shot.

This doesn't quite meet your explicit option, but one 3rd party option is
to use the LBL buildings library with something like open modelica.  The
library has a built-in comfort model (Fanger model), and you could build a
hydronic system around it.  Downside is the overhead in learning modelica,
and you will likely have to create a single-zone pet model to study the
problem in general terms.

Definitely an issue with current state of building modeling tools is the
slant towards new construction and fully functioning equipment.  I
shouldn't say issue because maybe this meets 90% of modeling needs?  But
those of us who live in the retrofit space run into these things all the
time.  What about a pneumatic thermostat that is leaking air and so is
causing a cooling valve to sit constantly at 80% open?  Or VFDs that are
put in hand at 40 HZ, or control valves that are manually overridden?

Aaron

On Fri, Jun 21, 2019 at 1:37 PM Nicholas Caton via Equest-users <
equest-users at lists.onebuilding.org> wrote:

> Apologies for the cross-post, however I wanted to ask this question from 2
> angles and I feel both communities may benefit from the discussion (if I
> can spark one).
>
>
>
> A common reality I’ve observed with “real-world” hydronic systems is that
> system coils and baseboard/radiator loops fall into a state coined *wild
> coils*.  Rather than modulating flow to maintain a measured supply air or
> room temperature setpoint, flow is *uncontrolled*.  A heating or reheat
> coil for example will end up dumping heat at all times the associated
> circulation loop is active, independent of its associated system’s fan
> operation, cooling coil activity, or thermostat signals requesting
> more/less heating.  Occupants in response to wild coils, when they cay,
> will end up using windows, propping open doorways, plugging in local space
> heaters / circ fans, and generally suffering in terms of comfort.  In just
> about every case, this scenario presents a win-win in terms of improved
> occupant comfort potential in parallel with energy savings potential for
> whoever is paying the bills.
>
>
>
> Causes for this situation I’ve encountered more than once include:
>
>    - Manual Control valves left in an open state, with dusty cobwebs
>    suggesting their presence is unknown to the occupants/building operators
>    - Automated valves (electric or pneumatic) which have become
>    mechanically stuck in an open, or partially open position
>    - Automated valves (electric or pneumatic) which are otherwise busted
>    due to upstream pneumatic line/system issues or mechanical failures of the
>    moving parts at the valve
>    - A valve was never designed and/or installed and/or wired up for
>    control in the first place
>
>
>
> For all of this however, I have always struggled in approximating the
> energy and comfort impacts of “wild” coils in my building energy
> simulations.  Quantifying this impact with some degree of confidence is
> difficult, but desirable in cases where I am calibrating to existing
> utility bills (read: always) and/or asserting the utility savings and
> comfort improvement impact for fixing/addressing such situations.
>
>
>
> *For the [bldg-sim] family:*  Are there any 3rd party tools, models, or
> other energy simulation platforms with explicit options for evaluating the
> comfort and energy impacts of wild coil situations?  Is there any research
> I could be pointed towards exploring this topic?
>
>
>
> *For the [eQuest-users] crowd:*  Can anyone share a best practice or
> recommendation for simulating this sort of problem-state within a
> doe2/eQuest model?  As far as I know, the native input options are
> essentially limited to a pair of “working” coil modulation states: TWO-WAY
> and THREE-WAY.  Here’s an example doe2 reference entry, with language that
> repeats a couple times over for different scenarios:
>
> I personally have taken different approaches, with none being particularly
> satisfactory.  These have included introducing process loads onto the loops
> concurrently with “free” internal energy source definitions to get those
> losses dumped into the spaces experiencing discomfort.  I have also played
> with artificially bumping the thermostat schedules around to reflect
> measured, uncomfortable temperature states…
>
>
>
> Any solutions/experiences/shared-commiseration would be very welcome!
>
>
>
> ~Nick
>
>
>
> [image: cid:image005.png at 01D515A3.47EDD880]
>
> *Nick Caton, P.E., BEMP*
>
>   Senior Energy Engineer
>   Regional Energy Engineering Manager
>
>   Energy and Sustainability Services
>   Energy Performance Contracting
>
> D
> M
> F
> E
>
> 913 . 564 . 6361
>
> 785 . 410 . 3317
>
> 913 . 564 . 6380
>
> *nicholas.caton at se.com <nicholas.caton at se.com>*
>
> 15200 Santa Fe Trail Drive
> Suite 204
> Lenexa, KS 66219
> United States
>
> [image: cid:image006.png at 01D515A3.47EDD880]
>
>
>
>
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