Hydronic System TAB Procedure

Hydronic System – TAB Procedure: by KHS Engineering Topics

Testing, Adjusting & Balancing (TAB) of hydronic system within HVAC systems; can be effectively accomplished by following the systematic methods & procedures describe in this article. The current recommended & best practices, which used in the industry for commonly installed hydronic systems, are discussed here.

There are many ways to accomplish the hydronic balancing of a system. Two most acceptable and common methods are,

1.       Proportional Balancing method (Ratio method)

2.       Stepwise Balancing method

 

Proportional Balancing (Ratio method)

The applying procedure of this method is varying based on the branches arrangement in the hydronic circuit.

 

Proportional Balancing Procedure – without Branch Circuits

a.       Verify & ensure that all balancing, control & isolation valves are fully open

b.       Follow an appropriate method and determine the total system volume/flow

c.        Identify the design flow and calculate the percentage of “Actual hydronic flow to Design flow requirements”

d.       Adjust the pump/s to approximately 110% of design flow, if possible with the available pump/s

e.       Proceed and measure the flow available at all balancing valves in the circuit

f.        Compute the ratio of measured flow to design flow for each terminal unit as per obtained balancing valve readings

g.       The balancing valve serving the terminal unit at the LOWEST percentage of design flow should not be adjusted. Identify this valve

h.       Adjust the balancing valve serving the terminal unit with the SECOND LOWEST percentage of design until both terminal units (Lowest & Second lowest) are the same percentage of design. These terminal units/valves are now in balance

i.         Proceed & adjust the balancing valve serving the terminal unit with THIRD lowest percentage of design until all three terminal units are at the same percentage of design and in balance

j.         This procedure need to be continue until all remainder terminals have been adjusted to be in balance at approximately the same percentage of design flow

k.       Re-measure all terminal units / valves and records the final value in TAB sheets

l.         All memory stops of the valves should be marked and lock the valves if the facility (DRV lock) available

 

Proportional Balancing – with Branch Circuits & Branch Balancing Valves

a.       Proceed & follow the first six steps (procedure for without branch circuits) for terminal units on each branch

b.       Compute the ratio of measured branch flow to design branch flow

c.        The balancing valve serving the branch at the LOWEST percentage of design flow should not be adjusted. Identify this valve

d.       Adjust the balancing valve serving the branch with the SECOND LOWEST percentage of design until both branches (Lowest & Second lowest) are the same percentage of design. These branches/valves are now in balance

e.       Proceed & adjust the balancing valve serving the branch with THIRD lowest percentage of design until all three branches are at the same percentage of design and in balance

f.        This procedure need to be continue until all remainder branches have been adjusted to be in balance at approximately the same percentage of design flow

g.       Then, proceed with proportioning steps given under “without branch circuit” for the terminal units on each branch

h.       All memory stops of the valves should be marked and lock the valves if the facility (DRV lock) available

 

Stepwise Balancing Method

The applying procedure of this method too is also varying based on the branches arrangement in the hydronic circuit.

 

Stepwise Balancing Method – without Branch circuits

a.       Verify & ensure that all balancing, control & isolation valves are fully open

b.       Follow an appropriate method and determine the total system volume/flow

c.        Identify the design flow and calculate the percentage of “Actual hydronic flow to Design flow requirements”

d.       Adjust the pump/s to approximately 110% of design flow, if possible with the available pump/s

e.       Proceed and measure the flow available at all balancing valves in the circuit

f.        Compute the ratio of measured flow to design flow for each terminal unit as per obtained balancing valve readings

g.       In general, the terminal units closer to pumping station are having the highest flow rate (less friction). Therefore, adjust the balancing valves of these units to a value approximately 10% below design flow requirements

h.       When the adjustment procedure reaches to end of the system/circuit the remaining terminal units flow values will increase

i.         Repeat the adjustment passes through the system until all terminal units are within ±10% of design flow requirements and at least one balancing vale remaining at fully open position

j.         Re-measure all terminal units / valves and record final values

k.       All memory stops of the valves should be marked and lock the valves if the facility (DRV lock) available

Stepwise Balancing Method – with Branch Circuits & Branch balancing valves

m.     Proceed & follow the first six steps (procedure for without branch circuits) for terminal units on each branch

n.       Compute the ratio of measured flow to design branch flow

o.       Follow the same procedures as detailed in above starting from the closest branch to the pumping station.

p.       Once all branches are completed proceed with terminal units of each branch as detailed above

 

Systems/Circuits with Self-Adjusting Valves (PICV / DPCV)

a.       Verify & ensure all balancing, control & isolating valves are fully open

b.       Follow an appropriate method and determine the total system volume/flow

c.        Identify the design flow and calculate the percentage of “Actual hydronic flow to Design flow requirements”

d.       Measure the differential pressure at each self-adjusting balancing valves

 

Complete Hydronic System Balancing Procedures

The overall balancing procedure for a hydronic system includes flow balancing & verification of relevant hydronic parameters. Such basic procedure, which can be apply to all types of hydronic distribution systems, is as below.

a.       Check, verify & ensure that all responsibilities of construction team from system installation to start-up are completed

b.       Verify & ensure all manual valves are open or pre-set as required (such as normally closed valves) and all temperature control (automatic) valves are in a normal or desired position

c.        Check, coordinate, verify & ensure that all automatically controlled devices within the hydronic circuit will not adversely affect the balancing procedure

d.       With the pump/s OFF observe/measure the static pressure at the pump/s

e.       Switch ON the pump/s, place the system into operation, check that all air has been vented from the piping system and allow flow condition to stabilize

f.        Check & verify that the system compression tank/s and automatic water fill valve mechanisms are operating & set correctly

g.       Measure & record the operating Voltage & Amperage of the pump/s and compare with nameplate rating literature and thermal overload heater ratings. Verify the rpm (speed) of each pump

h.       If flow meters or calibrated balancing valves are installed (which enable the flow rate measurement across the pump) perform the necessities and record the data

i.         Measure the “SHUT-OFF Head” of the operating pump by slowly closing a valve or balancing cock in the pump discharge piping. Record the discharge, suction pressure at the pump gauge connections, and determine the shut-off head. Preferably, one gauge should be used to read differential pressure. During this test, DO NOT close any valves in the discharge piping of a positive displacement pump. Severe damage may occur.

j.         With the use of measured shut-off head, determine and verify each pump’s impeller size and operating curve. Compare these data with pump design curves. If the test point falls on the design curve, proceed to the next step. If not, plot a new curve parallel with other curves on the chart from zero flow to maximum flow.

k.       Open the discharge-balancing valve slowly to the fully open position; record the discharge pressure, suction pressure & determine total operating head.

l.         Using the measured or calculated total operating head, read the pump water flow from earlier established corrected pump curve. If available, verify the pump curve data with data from flow meters and/or calibrated balancing valves

m.     If it comes to a scenario where measured total head is greater than the design, the flow will be lower than designed. If the measured total head is less than design, flow will be greater; in this scenario the pump discharge pressure is required to be increased by closing the discharge balancing valve where system flow align with approximately 110% of design

n.       Record the suction, discharge pressures & flow rate

o.       Prior to make any adjustment, an initial recording of the flow distribution throughout the system should be obtained. This can be performed with help of existing flow measuring devices or pressure/temperature port within the system. Also any balancing devices at equipment (chillers, boilers, heat exchangers, hot or chilled water coils)

p.       Proceed and obtain complete set of pressure drop measurements through all equipment and compare these with design data (equipment selection data sheets). Identify & get to know the circuits having high or low water flow. Generally, low circuits may be air bound. Vent the air if present in low circuits and repeat the readings

q.       Obtain actual total system flow & compare with design requirements

r.        Proceed with either proportional or stepwise balancing method (as detailed in earlier of this article) to adjust the flow rates through the equipment

s.        Upon completion of all final adjustments, proceed with a final check of the pressure and flow of all pumps & equipment. Re-measure the voltage and amperage of pump motors and record

t.        At the completion of all TAB works, set all memory stops and mark or score all balancing devices at final set points (locking the devices)

u.       Lastly, record final unit data, prepare the report forms and create the final report

 

Hydronic Systems with by-pass valves (Constant Flow systems)

Where by-pass valve or 3-way automatic valves are present, ensure the bypass flow is set to the specified values. If the specified flow is not available, adjust the by-pass flow to 90% of the design coil flow.

 

Hydronic Systems with Variable Flow

There is only a slight difference between in the TAB procedure for variable flow system compare with constant flow. The key difference: there is a mechanism exists within the system to vary the flow as per system demand.

Apart from above, discussed detailed steps following additional procedures should be used in balancing a variable flow hydronic system.

a.       Place the system in a simulated “full load” condition. If “diversity” is present in the system, temporary isolation of portions of the system piping and terminal units may be essential

b.       If the pump is controlled by a VFD, verify & ensure pump is operating at its rated speed prior to proceed with basic pump testing and flow measurement procedures as detailed previously

c.        Terminal units to be balanced following one of the methods described

d.       When diversity conditions are concerned, upon completion of balancing procedures with a portion of the system isolated, the isolated units should then be opened and an equal capacity of units to be closed

e.       Units isolated for the initial balancing procedure are then required to balance with design flow rates

f.        The values of variable flow control set-point/s to be measured and recorded. The HVAC system control specialist/contractor shall be provided with this information

Diversity is a design concept in a variable flow system that permits a system of terminal units to be fed by a pump that is rated for a fraction of the total system unit capacity. The TAB specialist should determine if the variable flow system has a diversity factor. The Diversity Factor is an arithmetic ratio of the pumps rated hydronic flow capacity divided by a summation of all terminal unit’s design maximum hydronic flow.

It is always a challenge and a tough task to balance a variable flow system with diversity, satisfactorily. Any TAB procedure applied will be a compromise and shortcomings will appear somewhere in the system under particular operation conditions. Expert fine-tuning is necessary after the initial TAB works are completed. This should be from proper coordination of designer, operator & TAB specialist.

 

Hydronic System with PRIMARY – SECONDARY Piping Arrangement

While performing the TAB works for this nature of systems, the initial balancing should be limited to the primary loop & its components. Secondary circuits/systems should be in full flow operation during primary circuit balancing works.

Below listed additional steps to be included in previously discussed general procedure.

a.       Place the primary circuit in simulated full load condition

b.       Proceed & conduct the basic pump testing and flow measurement procedures on primary circuit as discussed previously

c.        Place the secondary circuit/s in a simulated full load condition. As previously discussed if diversity is present in the system, temporary isolation of portions of system piping and terminal units should essential

d.       Proceed & conduct the basic pump testing & flow measurements for secondary circuit/s

e.       Proceed with the relevant balancing procedures & complete the TAB works

Above detailed similar procedure can be applied & practiced for Hydronic systems with Primary/Secondary/Tertiary circuits.

TAB works for Specific Systems

Previously discussed balancing procedures to be applied depend on the nature/type of the hydronic system. Below listed additional steps to be included while performing, the TAB works for specific types of hydronic distribution systems.

Condenser Water (Cooling Tower) Systems

Following steps to be applied with an open condenser water pumping station in operation.

a.       Proceed with basic pump testing & flow measurement procedures as detailed previously

b.       Check & record flow, inlet & outlet pressure readings of the tower piping (if the provisions are available). Compare with design data

c.        When a cooling tower bypass control is operational, measure the pressure difference with full condenser flow going both via tower & via the bypass line.

d.       Set the bypass line balancing valve to maintain a constant pressure at the pump discharge with the control valve in either position

The general TAB procedure for a Hydronic system in HVAC domain is discussed in this article. However, various water balancing tools & gadgets were introduced by different valve manufacturers (TA, Oventrop and etc…) over the last two decades; with the help of innovative technology associated. This helps remarkably reduce the higher time consume during the TAB works for hydronic systems in HAVC.

Even though you will use these tools today, the Engineering & Technical art behind the TAB process is something you should be aware.