Query Main Hot Water Loop - Stanford...

Query 9Main Hot Water LoopMain Hot Water Loop

Songya Kesler

Sangwoo ChoSangwoo Cho

06/03/2009

(1) Main Hot Water Loop

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Minimum = 25 Hz

From Utility

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Pressure = 125 psig

Temperature = 180 F

Steam supplied from the utility heats the water to the desired setpoint temperature. When heat is need, the 1/3 control valve opens first, then the 2/3 valve. Once the setpoint is reached the valves are slowly closed When hot water is needed the main hot waterreached, the valves are slowly closed. When hot water is needed, the main hot water pump is started. When hot water is no longer needed, the heat exchanger is closed and

shortly after, then pumps shut off.

(2) Point Summary Table

Since the only setpoint is the Supply Temperature, all other data points are either exogenous inputs or system responses, acting to maintain that setpoint temperature. Once again the valves control how much heat is supplied while the pumps control how muchagain, the valves control how much heat is supplied while the pumps control how much water is supplied to the system. The resulting flow rate, differential pressure, and return

temperature are results of these controls.

(3) Functional Requirements: Supply Temperature – Although the supply temperature appears to be different than the setpoint, this simply shows that

the setpoint is not what we previously assumed.

{Two days of data are missing in the middle week.

MAINHOTWATERLOOP: April 1st, 2009 to April 29th, 2009

(3) System Inputs: Steam from Utility – Through Bernoulli’s Equation, peaks in flow rate are matched by dips in pressure.


(4) System Response: Valve Position – The 1/3 valve is always sufficient to provide enough heat, so the 2/3 is never open. Open the valve more corresponds with faster flow ratesOpen the valve more corresponds with faster flow rates.


(4) System Response: Pump Speed – A single pump can maintain the necessary pump speed, so pumps are alternated every 7

days to maintain equal wear and teardays to maintain equal wear and tear.

Minimum Speed: 25 Hz


(4) System Response: Differential Pressure – The pressure difference is maintained at an estimated setpoint of 19.5 psi.

Estimated Setpoint: 19.5 psi


(5) Outcome Performance: Supply/Return Temperature Difference – The difference in temperature is inversely

proportional to the outside air temperatureproportional to the outside air temperature.


(5) Outcome Performance: Although the supply temperature does not seem to be related to the steam temperature, there is a

correlation with the valve openingcorrelation with the valve opening.


(5) Outcome Performance: Although the valve position increases both the waterflow rate and supply temperature, the two

themselves do not appear to be relatedthemselves do not appear to be related.


(6) System Evaluation

• The system as a whole is working well.• Only the Supply Temperature setpoint is below what is expected, but this simply indicates that the actual setpoint is closer to 150 Fthe actual setpoint is closer to 150 F.

• Supply/Return water temperature difference is inversely proportional to the outside airinversely proportional to the outside air temperature.

• As the valve opening widens, the supply p g , pp ytemperature and water flow rate increases.

• The two pumps effectively alternate every week.

GoodBad

GoodGood

(7) Comparison of Predicted/Measured Data

• 143 (Typical Office) – heating only, estimated occupancy levels and manually opened windows, no ceiling fans– Radiant heater 143 ‐ radiators are called “baseboards” in E+;Radiant heater 143 radiators are called baseboards in E+;

valve position (unavailable in E+) compared with simulated flow

• 145 (Representative Office) – same as 143( p )– Radiant heater 145 – same as RH143


The model assumes temperatures rise and decrease during occupied/unoccupied hours respectively. However, the temperature consistently fluctuates without any pattern.


In the model, a huge surge of water passes through the system early in the morning (in preparation for occupied hours); then at night, it comes to a complete stop. When the valve position is more open theposition is more open, the flowrate should increase shortly after. However, the flowratepeaks too quickly; if the valve

d l h h flopens steadily, then the flowrateshould increase steadily too.


Although the setup for rooms 143 and 145 are supposed to be the same, the simulated space t t f 143 i i dtemperature for 143 is organized while it is erratic for 145. Nonetheless, the simulated data is much more similar to the actual for room 145.

In comparing office 143 with 145, we believe that the difference can be attributed to differentattributed to different schedules used in the simulation.


As stated earlier, if the valve position opens gradually or quickly, then the flowrate should increase equally. This is evident in this comparison. The end points were not accounted for in the simulationthe simulation.


We are unsure as to why the simulated outlet temperature is so different than the actual HWso different than the actual HW return temperature. One thought is that the “outlet node” is in a different theoretical location than the actual return temperature sensor.


– Sometimes the model settings that most closely align with predicted data are not the same as the predictedwith predicted data are not the same as the predicted settings.

– Model settings are constant during the running g g gperiod, but the schedules are actually different day by day.

– Sometimes input simplifications lead to results that more closely follow the actual data than highly sophisticated inputssophisticated inputs.

– Examining larger periods of time may produce more meaningful patterns than hourly/daily periods.g p y/ y p

(8) Major Model ElementsElements Can Be

Modeled?Can BeAnalyzed in E+?

Interface?

W ll F ll h i ht ll YES YES W ll h i ht i tWall • Full‐height wall• Ceiling‐height wall• Fire‐rated wall• Non fire‐rated wall

YES YES •Wall height is not considered in analyzing.•Layers (e.g. GYB,

• Shaft wall• Openings (doors/windows)• etc

y ( g ,insulation, etc) do not have thickness in analyzing.

Slab • Concrete• Steel

YES YES

Roof YES YES • Roof material is t id d inot considered in

analyzing.

Ceiling • Acoustic• Gypsum

YES YES• Gypsum

Column/Beam

• Concrete• Steel

YES YES

(8) Major Model ElementsElements Can Be

Modeled?Can BeAnalyzed in E+?

Interface?

Mechanical • Med & Low Pressure Ducts• Branches Ducts• CAV & VAV Boxes

YES YES • Insulation (typically 2”) is not considered i l iin analyzing.

Electrical • Cable Tray• Conduit Racks• Light Fixtures

YES NO

• Light FixturesPlumbing • Plumbing Pipes

• Mech Pipes• Gravity Lines

YES NO

y

Fire Piping • Sprinkler Mains• Sprinkler Drops

YES NO

Support/ YES NOSupport/ Seismic

YES NO

(8) Five Rules

• Sequence Rule: Before examining the data, have a strong grasp of the sequence of operations as you move along datagrasp of the sequence of operations as you move along data points in the system.

• Setpoint Rule: If there is a setpoint, the data should be plotted around that value.

• Occupancy Rule: Between occupied and unoccupied hours, certain data points should rise and fall accordinglycertain data points should rise and fall accordingly.

• Consistency Rule: Depending on data type, it may follow a predictable pattern. p p

• Big Picture Rule: Although there may be a discrepancy in one point, examine other points in the system (or nearby) because the ma correlatethey may correlate.

Query Main Hot Water Loop - Stanford...

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