Chilled Water Meter Assistance Needed
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Posts: 46,084
Hello Everyone!
My employer (University of Texas) needs to find someone to create a
chilled-water usage meter. There is a hardware and a software component to
this task. I anticipate that a BASIC Stamp would be the brains of the
device. Can anyone suggest someone to do the software, the hardware, or
both? We would want to purchase, not license, the software, and we would
want fully-commented source code.
===
SUMMARY
We need to purchase about 10 to 20 units for measuring chilled-water usage
(for billing purposes). Payment by credit card would be easiest, or if you
can invoice the University payment by check can be made.
BACKGROUND
The University of Texas uses chilled water for air conditioning its
buildings. Some self-supporting buildings pay for the chilled water (like
they pay for power and water). We need to know how much to bill them each
month.
The basic formula is that tons of cooling = flowrate (gpm) x delta
temperature (out - in) x a factor (F4). We sell ton-hours of cooling, so
this calculation could be made every hour and then the products summed over
a month. Using a BASIC Stamp, the calculation might be done every second.
The flowrate data is available as a voltage, 0.5 to 2.5 volts. This is
actually derived from a 4 to 20 mA signal. Voltages under 0.5 are not
allowed. Voltages of 0.5 to 2.5 scale directly with the flowrate, in gpm.
(GPM = Voltage x F1)
The delta-temperature is available as a voltage, 0.5 to 2.5 volts. Voltages
under 0.5 are not allowed. Voltages of 0.5 to 2.5 are linearly related to
the delta-temperature, in degrees F. (0.5 volts equals F2 degrees, 2.5
volts equals F3 degrees, everything in between is linear, some buildings
have F2=-5 and F3=+25 degrees)
We believe that 8 bit A-D conversion is adequate.
Every second we need to multiply the gpm x degrees x factor F4, add it to
the running total, and display the running total on an LCD.
Every month a person will write down the displayed digits. By subtracting
from last month's displayed numbers, we will know the ton-hours used by the
building. The long-term plan is to read the flow and delta-temperature by
network and do the calculations in a facilities management computer.
Factors F1, F2, F3 will vary from building to building. F4 is related to
the sampling frequency.
FEATURE CREEP
It would be nice to be able to push a button and have the display show the
flowrate (gpm) and the delta-temperature (degrees F). Or, use a display
that can show running total, gpm and delta-temperature simultaneously...the
Scott 2x16 LCD units look good.
It might, or might not, be desirable to be able to modify the variables in
the field. It should not be easy for an uninitiated person to make this change.
===
That's about it. Can anyone suggest a person or company to do this?
Thank you!
Miles Abernathy, miles@m...
512-471-1600 voice, 603-452-9188 fax
PS-Everyone thinks, "You're a big university, get a student to do it." This
has turned out to be difficult to do, and we would like to find someone not
encumbered by homework to do the work.
My employer (University of Texas) needs to find someone to create a
chilled-water usage meter. There is a hardware and a software component to
this task. I anticipate that a BASIC Stamp would be the brains of the
device. Can anyone suggest someone to do the software, the hardware, or
both? We would want to purchase, not license, the software, and we would
want fully-commented source code.
===
SUMMARY
We need to purchase about 10 to 20 units for measuring chilled-water usage
(for billing purposes). Payment by credit card would be easiest, or if you
can invoice the University payment by check can be made.
BACKGROUND
The University of Texas uses chilled water for air conditioning its
buildings. Some self-supporting buildings pay for the chilled water (like
they pay for power and water). We need to know how much to bill them each
month.
The basic formula is that tons of cooling = flowrate (gpm) x delta
temperature (out - in) x a factor (F4). We sell ton-hours of cooling, so
this calculation could be made every hour and then the products summed over
a month. Using a BASIC Stamp, the calculation might be done every second.
The flowrate data is available as a voltage, 0.5 to 2.5 volts. This is
actually derived from a 4 to 20 mA signal. Voltages under 0.5 are not
allowed. Voltages of 0.5 to 2.5 scale directly with the flowrate, in gpm.
(GPM = Voltage x F1)
The delta-temperature is available as a voltage, 0.5 to 2.5 volts. Voltages
under 0.5 are not allowed. Voltages of 0.5 to 2.5 are linearly related to
the delta-temperature, in degrees F. (0.5 volts equals F2 degrees, 2.5
volts equals F3 degrees, everything in between is linear, some buildings
have F2=-5 and F3=+25 degrees)
We believe that 8 bit A-D conversion is adequate.
Every second we need to multiply the gpm x degrees x factor F4, add it to
the running total, and display the running total on an LCD.
Every month a person will write down the displayed digits. By subtracting
from last month's displayed numbers, we will know the ton-hours used by the
building. The long-term plan is to read the flow and delta-temperature by
network and do the calculations in a facilities management computer.
Factors F1, F2, F3 will vary from building to building. F4 is related to
the sampling frequency.
FEATURE CREEP
It would be nice to be able to push a button and have the display show the
flowrate (gpm) and the delta-temperature (degrees F). Or, use a display
that can show running total, gpm and delta-temperature simultaneously...the
Scott 2x16 LCD units look good.
It might, or might not, be desirable to be able to modify the variables in
the field. It should not be easy for an uninitiated person to make this change.
===
That's about it. Can anyone suggest a person or company to do this?
Thank you!
Miles Abernathy, miles@m...
512-471-1600 voice, 603-452-9188 fax
PS-Everyone thinks, "You're a big university, get a student to do it." This
has turned out to be difficult to do, and we would like to find someone not
encumbered by homework to do the work.
Comments
http://home.fuse.net/leroy/resume.htm
Let me know if you are interested.
LeRoy
Miles Abernathy wrote:
>
> Hello Everyone!
>
> My employer (University of Texas) needs to find someone to create a
> chilled-water usage meter. There is a hardware and a software component to
> this task. I anticipate that a BASIC Stamp would be the brains of the
> device. Can anyone suggest someone to do the software, the hardware, or
> both? We would want to purchase, not license, the software, and we would
> want fully-commented source code.
>
> ===
> SUMMARY
> We need to purchase about 10 to 20 units for measuring chilled-water usage
> (for billing purposes). Payment by credit card would be easiest, or if you
> can invoice the University payment by check can be made.
>
> BACKGROUND
> The University of Texas uses chilled water for air conditioning its
> buildings. Some self-supporting buildings pay for the chilled water (like
> they pay for power and water). We need to know how much to bill them each
> month.
>
> The basic formula is that tons of cooling = flowrate (gpm) x delta
> temperature (out - in) x a factor (F4). We sell ton-hours of cooling, so
> this calculation could be made every hour and then the products summed over
> a month. Using a BASIC Stamp, the calculation might be done every second.
>
> The flowrate data is available as a voltage, 0.5 to 2.5 volts. This is
> actually derived from a 4 to 20 mA signal. Voltages under 0.5 are not
> allowed. Voltages of 0.5 to 2.5 scale directly with the flowrate, in gpm.
> (GPM = Voltage x F1)
>
> The delta-temperature is available as a voltage, 0.5 to 2.5 volts. Voltages
> under 0.5 are not allowed. Voltages of 0.5 to 2.5 are linearly related to
> the delta-temperature, in degrees F. (0.5 volts equals F2 degrees, 2.5
> volts equals F3 degrees, everything in between is linear, some buildings
> have F2=-5 and F3=+25 degrees)
>
> We believe that 8 bit A-D conversion is adequate.
>
> Every second we need to multiply the gpm x degrees x factor F4, add it to
> the running total, and display the running total on an LCD.
>
> Every month a person will write down the displayed digits. By subtracting
> from last month's displayed numbers, we will know the ton-hours used by the
> building. The long-term plan is to read the flow and delta-temperature by
> network and do the calculations in a facilities management computer.
>
> Factors F1, F2, F3 will vary from building to building. F4 is related to
> the sampling frequency.
>
> FEATURE CREEP
> It would be nice to be able to push a button and have the display show the
> flowrate (gpm) and the delta-temperature (degrees F). Or, use a display
> that can show running total, gpm and delta-temperature simultaneously...the
> Scott 2x16 LCD units look good.
>
> It might, or might not, be desirable to be able to modify the variables in
> the field. It should not be easy for an uninitiated person to make this
change.
> ===
>
> That's about it. Can anyone suggest a person or company to do this?
>
> Thank you!
>
> Miles Abernathy, miles@m...
> 512-471-1600 voice, 603-452-9188 fax
>
> PS-Everyone thinks, "You're a big university, get a student to do it." This
> has turned out to be difficult to do, and we would like to find someone not
> encumbered by homework to do the work.
--
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