Common control valve installation diagrams, The Benefits of Return Side Control Valve Installation. Anything that changes the flow resistance of the distribution system causes the system curve to either steepen, (for increasing flow resistance), or flatten (for decreasing flow resistance). 0000402841 00000 n For those that don't, you can determine the differential pressure across the system when all zones are operating by finding the head at the operating point and converting it to a differential pressure using Formula 1. 0000680653 00000 n In a heating application, the water temperature leaving the coil is cooler than the supply temperature. This causes heat input to zones that are supposed to be off. Far superior method of linking multiple heat sources. When a zone valve closes, the system curve steepens forcing the operating point to slide upward along the pump curve. True, they do prevent the circulator from operating at high differential pressures and, hence, eliminate flow noise and valve seat leakage. The system can be harder to design, requiring both "SPDT" thermostats or relays and the ability of the system to withstand the fault condition whereby all zone valves are closed simultaneously. No inherent redundancy for the pump. When a zone valve closes less heat is released by the distribution system and, hence, the temperature drop from the supply to return header drops. Assume all the circuits are controlled by zone valves. 0000428586 00000 n Such circulators have been used in Europe for several years, and will soon gain market share in North America. When a control valve is installed on the return side, the water is at a higher pressure through the coil, reducing off-gas, thereby lowering dissolved oxygen content compared to a supply installation. 1999 - 2022 BELIMO AIRCONTROLS (USA), INC. ALL RIGHTS RESERVED, Caribbean, Latin America, and United States, Terms and Conditions of Sale and Warranty, Pressure Independent Valves Simplifies Balancing and Saves Energy, Improving Campus Chilled Water Systems with Intelligent Valves, New Belimo Energy Valve to Release May 25th. In this case, the valve is normally closed by the force of the spring but can be opened by the force of the wax motor. 0000008923 00000 n To determine the differential pressure across the circulator, draw a horizontal line from the operating point to the vertical axis and read the head added to the fluid as it passes through the circulator. 0000012702 00000 n 0000681200 00000 n 0000682407 00000 n What remains is for manufacturers to develop a simple, low-cost differential pressure sensor that can serve as the eyes for the circulator, telling it when and by how much to vary its speed. A good way to visualize this phenomenon is by opening a carbonated beverage bottle; the sudden pressure drop allows the entrapped carbonated gas to come out of the solution and quickly dissipate. Visit our updated. 0000008370 00000 n 0000008059 00000 n As the zone valves open and close and the system curve changes its "steepness," the pump curve of a variable speed circulator can be shifted as necessary to maintain the same differential pressure across the operating zones. At least two major pump manufacturers now have small variable speed circulators on the market. A more elegant solution to controlling differential pressure as zone valves close is to reduce the speed of the circulator. 0000001786 00000 n A zone-valved system is dependent upon a single circulator pump. 0000003230 00000 n The zones that remain on don't sense that other zones have closed. The overall system flow rate decreases, but the flow rate through each open zone circuit increases. As the system curve shifts so does the point where it intersects the pump curve. By closing this message or continuing to use our site, you agree to the use of cookies. A zone valve is a specific type of valve used to control the flow of water or steam in a hydronic heating or cooling system. ASHRAE states that "water velocity noise is not caused by water, but by free air, sharp pressure drops, turbulence, or a combination of these, which in turn cause cavitation or flashing of water into steam" (2009 ASHRAE Fundamentals Handbook, Chapter 22). Multiple zones can be implemented using either multiple, individually controlled circulator pumps or a single pump and multiple zone valves. As zone valves close, the bypass valve shuttles increasing amounts of flow through a piping detour rather than forcing the pump to operate at higher pressure differentials trying to push flow through a more restrictive distribution system. 0000681339 00000 n For webinar sponsorship information, visit www.bnpevents.com/webinars or email webinars@bnpmedia.com. Under design load conditions all space heating zones should, theoretically, need heat, and thus all zone valves should be open simultaneously. If the water pressure is reduced, the air is released. Variable speed circulators prevent changes in differential pressure and reduce electrical energy use in the process. Operating circulators draw more power any time the zone is actively heating. It would be a straight horizontal line at some fixed value of differential pressure. Figure 2 shows this effect for a system having several identical floor heating circuits each controlled by its own zone valve. For vacuum- or pneumatically operated zone valves, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded rubber diaphragm to move and actuate the valve. 0000404082 00000 n The pressure drop results in air entrapment on the leaving side of the coil. In both cases the zone circuits that remain on "feel" increased differential pressure as the other zones close, but far less in the system using the circulator with the flat pump curve. When represented on a graph, the system always operates at the point where the system curve crosses over the pump curve as shown in Figure 3. Circulator pumps cost more than zone valves. Immediately following that moment of uncertainty they invoked the ever-popular bigger-is-better selection criteria. The system curve of the distribution system steepens each time a zone valve closes. 0000003799 00000 n Return side installations may not always be appropriate, as in the case of a 3-way diverting valve- these are commonly installed on the supply and is not critical to proper operation; both locations will work effectively. In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to cool down. A control valve in a closed-loop circuit, Cv, is often calculated with an equal or greater than drop to than the coil. Higher initial installation cost. 0000012841 00000 n If it fails, the system becomes completely inoperable. Design, CMS, Hosting & Web Development :: ePublishing. 0000680552 00000 n The domestic water heater is likely to be the only zone operating during warm weather. Just like a circulator with the "ideal" pump curve we discussed earlier. / cubic ft. for 140-degrees F water). %PDF-1.3 % They should also be used to prevent "dead heading" the circulator in systems where several parallel-piped heat emitters are controlled by thermostatic radiator valves. Some of the lanes on the bridge are now blocked off, and it's simply not possible to get the same amount of traffic across, even though traffic moves slightly faster along each lane. In a chilled water application, the tempered water of the return reduces the amount of potential condensate on the valve from reaching the actuator. 0000006931 00000 n John Siegenthaler, P.E., is a consulting engineer and principal of Appropriate Designs in Holland Patent, New York. Removal of electrical power re-closes the valve. Visit our updated, This website requires certain cookies to work and uses other cookies to help you have the best experience. This website requires certain cookies to work and uses other cookies to help you have the best experience. Higher power consumption. What is your most successful way of finding employees? Figure 4 shows the curve of such a circulator as well as the curve of a "high head" circulator. John Siegenthaler: Don't forget about ventilation, John Siegenthaler: Combining an air-to-water heat pump with a heated floor slab, John Siegenthalers Top 25 most-read articles, John Siegenthaler: Modern biomass meets state-of-the-art hydronics, John Siegenthaler: 5 products the hydronics industry needs, Whatever's On The Truck
John Siegenthaler, PE. In either case, the motor is usually connected to the water valve via a mechanical coupling. Zone valves can also be constructed using wax motors and a spring-return mechanism. 0000007505 00000 n Hb```g``U``cgb@ !V(GT *`jzAd:kEXj>2(=`Lapi``ePT` ex+ ".f,`9Pu}# \` pCPnw@ b|, endstream endobj 68 0 obj 208 endobj 28 0 obj << /Type /Page /Parent 13 0 R /Resources 29 0 R /Contents 35 0 R /MediaBox [ 0 0 666 855 ] /CropBox [ 0 0 666 855 ] /Rotate 0 >> endobj 29 0 obj << /ProcSet [ /PDF /Text /ImageC ] /Font << /F1 31 0 R /F2 40 0 R /F3 38 0 R /F4 39 0 R /TT1 30 0 R >> /XObject << /Im1 51 0 R /Im3 53 0 R /Fm2 61 0 R >> /ExtGState << /GS1 45 0 R /GS2 46 0 R /GS3 62 0 R >> /ColorSpace << /DefaultCMYK 34 0 R /Cs8 34 0 R >> /Properties << /MC1 64 0 R /MC2 66 0 R >> >> endobj 30 0 obj << /Type /Font /Subtype /TrueType /FirstChar 32 /LastChar 133 /Widths [ 278 296 389 0 0 0 815 204 333 333 0 0 278 333 278 0 556 556 556 556 556 556 0 0 556 556 0 0 0 0 0 444 0 722 722 722 778 722 667 0 0 407 0 0 667 0 0 778 0 0 722 630 667 815 0 981 0 704 0 0 0 0 0 0 0 556 556 444 574 500 333 537 611 315 296 593 315 889 611 500 574 556 444 463 389 611 537 778 537 537 481 0 0 0 0 0 0 0 0 0 0 1000 ] /Encoding /WinAnsiEncoding /BaseFont /CMGENC+CenturySchoolbook /FontDescriptor 32 0 R >> endobj 31 0 obj << /Type /Font /Subtype /Type1 /FirstChar 32 /LastChar 133 /Widths [ 352 512 577 704 704 1027 898 352 449 449 448 694 352 449 352 577 704 704 704 704 704 704 704 704 704 704 352 352 694 694 694 642 924 834 834 705 834 705 705 770 834 451 577 834 642 1027 834 834 834 834 834 704 707 834 770 1027 834 770 705 449 577 449 694 500 321 770 770 642 770 770 512 770 770 385 385 705 385 1155 770 770 770 770 512 642 577 770 705 1027 770 705 642 449 256 449 694 0 0 0 0 0 0 1000 ] /Encoding /WinAnsiEncoding /BaseFont /CMGENB+AntiqueOlive-Compact /FontDescriptor 33 0 R >> endobj 32 0 obj << /Type /FontDescriptor /Ascent 985 /CapHeight 0 /Descent -216 /Flags 34 /FontBBox [ -165 -307 1246 1201 ] /FontName /CMGENC+CenturySchoolbook /ItalicAngle 0 /StemV 0 /FontFile2 49 0 R >> endobj 33 0 obj << /Type /FontDescriptor /Ascent 746 /CapHeight 714 /Descent -136 /Flags 32 /FontBBox [ -164 -136 1147 972 ] /FontName /CMGENB+AntiqueOlive-Compact /ItalicAngle 0 /StemV 254 /XHeight 601 /StemH 254 /CharSet (/A/W/e/t/space/r/u/n/s/a/d/z/o/v/l/ellipsis/g/exclam) /FontFile3 43 0 R >> endobj 34 0 obj [ /ICCBased 47 0 R ] endobj 35 0 obj << /Length 3057 /Filter /FlateDecode >> stream All active zones operate at the same flow rate and differential pressure regardless of which zones are off. A single circulator pump and zone valves. This style of valves requires the use of an SPDT thermostat or relay. trailer << /Size 69 /Info 24 0 R /Root 27 0 R /Prev 1231052 /ID[<6d5752131d918b84c73a5def00ee22e0>] >> startxref 0 %%EOF 27 0 obj << /Type /Catalog /Pages 13 0 R /Metadata 25 0 R /JT 23 0 R /PageLabels 12 0 R >> endobj 67 0 obj << /S 95 /L 225 /Filter /FlateDecode /Length 68 0 R >> stream In some systems the increased differential pressure generated by several inactive zones can partially open what are supposed to be closed zone valves. If flatter is better, what do you think an "ideal" pump curve would look like? Unlike the electrical zone valves, these valves automatically return to the default position without the application of any power, and the default position is usually "open", allowing heat to flow. This valve works like a pressure relief valve that "relieves" flow back to the intake side of the circulator rather than to a drain. Still, I wish I had a dollar for every time someone installed a "high head" pump in a system containing several zone valves, and eventually heard about the problem - literally! The return side is preferable as it allows the valve and actuator to operate at a reduced temperature which can help protect valve seats and actuator electronics over the installation lifetime. Zone valves operated by electric timing motors aren't "fail safe" (failing to the "open" condition). 0000001611 00000 n 0000002633 00000 n 0000009223 00000 n Each approach has advantages and disadvantages. In most cases I would bet the installer didn't know if a standard 1/25 horsepower circulator had enough "humph" for a system with more than three or four zones. A zone valve is arguably one of the most commonly used control components in residential and light commercial hydronic systems. Afterward, convert that head gain to a differential pressure using Formula 1. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. The first principle to understand is that the amount of air in the water at a given temperature depends on pressure. When you adjust a differential pressure bypass valve set the knob so the disc just starts to lift away from its seat when all zone valves are open, then increase the differential pressure setting just a tad. This increases the pressure differential imposed on the zones that remain open. As the speed decreases, the pump curves shifts to the left and downward on the graph as shown in Figure 6. RU2ghxE>|m;OH[TK+9)N~Ao )hoJMllj1/c@byK'i`jG)F][^ ?L'BcV9`NSX?|&. 0000680270 00000 n Simple mechanical and control design ("SPST thermostats"). This decreased dissolved oxygen content minimizes air entrapment or free air in the coil and thus the potential for noise. (Q|g#7} All Rights Reserved BNP Media. Another technique for limiting the differential pressure across the circulator is to install a differential pressure bypass valve as shown in Figure 5. However, they do so by throttling away head energy rather than reducing electrical power input to the circulator. It's been described in many references over several decades for those willing to learn how to properly select hydronic circulators. 0000529578 00000 n 26 0 obj << /Linearized 1 /O 28 /H [ 1312 320 ] /L 1231700 /E 683706 /N 2 /T 1231062 >> endobj xref 26 43 0000000016 00000 n The temperature sensors associated with the pump controller sense this change as it develops and reduces the speed of the pump downward to maintain a set temperature drop. 0000679965 00000 n In my opinion a differential pressure bypass valve should be used in any zone valve system or sub-system that contains more than four zones or uses a circulator having a rating greater than 1/25 horsepower. Zone valves are inherently more unreliable and prone to a very high failure rate. 0000683357 00000 n Comparison with multiple circulator pumps, Learn how and when to remove this template message, https://en.wikipedia.org/w/index.php?title=Zone_valve&oldid=891891377, Articles lacking sources from January 2008, Creative Commons Attribution-ShareAlike License 3.0. For electrical zone valves, the motor is often a small shaded-pole synchronous motor combined with a rotary switch that can disconnect the motor at either of the two stopping points ("valve open" or "valve closed"). 0000003447 00000 n Imagine, for example, a system having several zoned space heating circuits and a separate circuit supplying an indirect water heater. In large commercial installations, vacuum or compressed air may be used instead. Also shown are progressively steeper system curves that represent zone valves closing off in the system. You could also install pressure gauges on the supply and return sides of the distribution system to determine the pressure differential when all zones are operating. Additional information and resources for hydronic system design are available on Siegenthalers website, www.hydronicpros.com. Compare the changes in differential pressure as the operating point shifts upward along the "flat" pump curve to those that would occur along the pump curve of the high head circulator. It's possible that a high differential pressure across the circulator when the DHW load is operating could lead to hot water "oozing" through the closed zone valves on the space heating circuits.