simplifying hydronic systems picvs - rses.org

Pressure-independent

control valves used with

hydronic-based heating

provide an opportunity for

increased chiller efficiency

and, if paired with a vari-

able-speed drive, reduced

operating costs.

B y E d w i n H i P o l i t o

w w w . r s e s j o u r n a l . c o m

this cross-section of a PiCV shows theflow through the valve.

16 RSES Journal OCTOBER 2010

Simplifying

Today, as the United States seeks to reduce the consumption of en-ergy—and the country’s dependence on foreign sources for that energy—the building sector is the subject of extra attention as the

industry seeks to increase building energy efficiency and reduce energy usage.

One particular area that requires examination is improvement of a building’s energy consumption through a hydronic-based HVAC system. This system incorporates a variety of pump sizes that deliver the required hot or chilled water to various locations within the building. Ideally, the system effectively meets load requirements throughout the building.

In reality, the system tends to deliver load requirements inconsistent-ly, resulting in wasted energy. And while energy is wasted, equipment ef-ficiencies are lowered, building temperatures are not met, and tenant dis-comfort complaints are directed to facility mangers.

The inefficient system also contributes to wasted time and effort, as well as increased operating costs. In an effort to address this situation, components are often incorporated into the system to provide increased system efficiency and control.

with

PICVsHydronic Systems

All images courtesy of Danfoss

w w w . r s e s j o u r n a l . c o m

this cross-section of a PiCV shows theflow through the valve.

Figure 1 this figure illustrates automatic balancing in the lower-half and temperature control in the upper-half together in one valve.

OCTOBER 2010 RSES Journal 17

Circle Reader Service No. 50

One of these components—a pressure-independent con-trol valve—provides an opportunity for an increase in chiller efficiency and, if paired with a variable-speed drive, further reduces operating costs.

Proper balancingBuilding designs often incorporate balancing valves to pro-vide proper flow to the emitter or terminal unit, and help meet room load requirements. Without proper balancing, overflows contribute to inefficiencies that are the result of ex-cess power consumption by the pump due to the system’s de-creased energy transfer.

Manual-balancing valves improve this situation by main-taining proper flows during peak design conditions. However, based on outside conditions and time of day, load require-ments are rarely at design conditions, reducing the effective-ness of the manual balancing valve.

The commissioning of these traditional valves requires a fair amount of involvement and coordination to meet the pre-calculated and actual requirements of the system. As valves are adjusted, the balancer must be aware of the re-quirements for a particular location and the effect they will have on the system as a whole. After startup, comfort-related service calls may be necessary to fine-tune the valves. As a result, a manual-valve-based system requires a significant in-vestment in time and effort when compared to PICVs, which offer a practical alternative to system balancing.

In contrast to static manual balancing valves, PICVs dy-namically adjust to system pressure changes. A PICV valve is designed to maintain a constant pressure difference through the integrated temperature control valve by means of a dif-ferential pressure regulator. As seen in Figure 1, P1 reflects the incoming pressure from the system and P3 is the outlet pressure from the temperature-control valve, which regulates the amount of fluid required for the room temperature. In-

between these two pressures is P2, which regulates itself, via its mechanism, to ensure the pressure across the temperature- control orifice remains constant even though there are pres-sure increases or decreases as a result of flow and pump speed

All images courtesy of Danfoss

w w w . r s e s j o u r n a l . c o m OCTOBER 2010 RSES Journal 19


changes in the system. A constant differential pressure across the temperature-control valve ensures a proper flow rate from the PICV, providing a significant improvement over systems installed with manual balancing valves.

The ability to adjust and maintain consistent flows in-creases output efficiencies from equipment and emitters, and

leads to improved control of room temperature and reduced costly service calls. [Note: The changes in the system are relat-ing to system pressure changes. There are several other variables associated in achieving efficiency that are not discussed in depth in this article relating to control theory from the valve assembly for the system. The ability of the valve to adjust itself to provide

these larger-flanged PiCVs are used in commercial applications.


w w w . r s e s j o u r n a l . c o m20 RSES Journal OCTOBER 2010

a constant differential pressure through the integrated tempera-ture-control valve allows the temperature control to better meet/ match the required load adjustments.]

Real-world controlConsider a building during a mid-day cooling scenario where

the north side of the building experiences reduced cooling demands and a manual-balancing valve and control valve setup is in place. The reduced requirements on the north side of the building mean the majority of flow is directed to south-side emitters, creating an increased differential pres-sure situation. As a result, the control valve must work twice

Piping comparisons be-twen traditional and PiCV installation on air-handling unit or VAC unit.

w w w . r s e s j o u r n a l . c o m22 RSES Journal OCTOBER 2010

as hard to simultaneously adjust for the variable differential-pressure and

room-temperature demand. This scenario leads to

an erratic response from the controller and un-even temperature con-

trol. The addition of a VFD with high- and low-

load conditions and the in-ability of proper control through a manual-balancing valve and con-trol the valve further compounds

the problem. With the installation of a PICV, the majority of control for various system situations will be close to ideal conditions.

In addition to improvements to the control of the system, the PICV—as part of a hydronic system—contributes benefits relating to the valve assembly installation and commissioning. Current product offerings of PICVs are designed to integrate two conventional installed components into one—a manual valve and control valve.

These traditional installed valves typically require space to accommodate the valves and fittings. The PICV improves upon this traditional setup by combining aspects of balancing and control into a single compact valve. And, by incorporat-ing a self-regulating differential pressure regulator within the valve, the benefits of the system multiply to include reduced installation time, decreased piping area and less potential for leakage related to fittings.

Time savings also can be achieved during commis-

sioning of the assembly. The valve’s ability to self-regulate re-

duces the need for service calls to fine tune the valve after initial commis-

sioning. The design of the internal mecha-nism makes commissioning dependent on

the installed valve’s required-design flow rate and maximum-flow-rate capability. After calculating the re-quired percentage of the maximum flow rate, the PICV can be set, and the commissioning of the valve is complete. The straightforward setting of the PICV reduces the effort in-volved to cross-reference the information with a system’s cal-culated and actual value requirements. This set-it-and-forget-it ability to commission PICVs improves the time required to properly balance the system.

Overall, PICVs represent an improvement over conven-tional manual-balancing valves by offering constant flow regulation to the system and contributing to an ideal design situation. This, in turn, leads to efficient outputs, reduced en-ergy consumption and lower costs to operate the system. As efforts to achieve energy efficiency are becoming the norm, the PICV provides the opportunity to meet those challenges efficiently and effectively.

Edwin Hipolito is the Applications Engineer at Danfoss, where he has worked with the Hydronics Control Division for more than eight years. For more information on PICVs, visit www.na.heating.danfoss.com.

In addition to improvements to the control of the system, the PICV—as part of a hydronic system—

contributes benefits relating to the valve assembly installation and commissioning.

“ this is an example of a

PiCV assembly used in larger-sized pipe applications.

this is an example of a smaller-sized PCiV used for a fan-coil or

VAV application.

simplifying hydronic systems picvs - rses.org

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