"Best Practices in Modern Hydronic Heating - THE DETAILS

Transcription

1 "Best Practices in Modern Hydronic Heating - THE DETAILS 190 supply water temperature (ºF) fin-tube convector (RR=1.38) panel radiator (RR=1.0) thin slab rad. floor (RR=0.69) slab r adian t floor (RR=0.31) 180 ºF 150 ºF 125 ºF 105 ºF T 1 f 1 f 2 T 3 NOTE: f 1 = f 3 (always!) NOTE: f 2 = f 4 (always!) f 3 f 4 T 2 T 4 300,000 Btu/hr! mod/con boiler! (fixed lead stage) Outdoor outdoor temperature (ºF) 2014 presented by: John Siegenthaler, P.E. Appropriate Designs Holland Patent, NY Copyright 2014, J. Siegenthaler, all rights reserved. The contents of this file shall not be copied or transmitted in any form without written permission of the author. All diagrams shown in this file on conceptual and not intended as fully detailed installation drawings. No warranty is made as the the suitability of any drawings or data for a particular application. 100,000 Btu/hr 100,000 Btu/hr conventional boilers for stages 2 and 3! (these boilers rotate in firing order)

2 "Best Practices in Modern Hydronic Heating - AN OVERVIEW This Afternoon s topics... Multiple mod/con boiler systems Hydraulic separation Distribution efficiency Applying high efficiency circulators Outdoor reset control Hydronic approaches to on-demand domestic water heating short fat

3 Multiple modulating / condensing boilers The new normal in commercial boiler systems

4 Multiple modulating / condensing boilers The evolution of an old hydronic system

5 Multiple modulating / condensing boilers The evolution of an old hydronic system multiple! boiler! controller outdoor! temperature! sensor supply! temp.! sensor hydraulic! separator from existing system sediment capture! and removal

6 Multiple modulating / condensing boilers Multiple modulating / condensing boilers, combining staging and modulation Minimum heat output OFF OFF OFF 20% % modulation 100% 75% 50% 25% SERIES staging/modulation boiler #3 boiler #2 boiler #1 0% increasing heating load 100% PARALLEL staging/modulation Heat output = 30,000 Btu/hr % modulation 75% 50% 25% 0% Maximum heat output 100% 100% 100% 100% 100% increasing heating load HYBRID staging/modulation % modulation 75% 50% 25% 0% increasing heating load Heat output = 600,000 Btu/hr 600,000 Btu/hr system turndown ratio = 30,000 Btu/hr = 20/1

7 Multiple modulating / condensing boilers Typical European concepts for multiple mod/con installation:

8 What did you notice in common on those last two photos? Modular manifold system - could be expanded if necessary Hydraulic separator interface to system Pre-engineered racking systems individual circulators on each boiler Polypropylene manifolded venting multiple! boiler! controller outdoor! temperature! sensor supply! temp.! sensor hydraulic! separator to / from! loads

9 Boiler manifold with integral hydraulic separator (courtesy Sinus North America). Form fitting insulation is supplied with all manifolds. Flexible piping connects each boiler to low manifold. (Boilers have integral circulators and check valves.) Notice that two additional boilers can be added to the front side of lower manifold.

10 Here's what the real products look like

11 How about 8 mod/cons with integral hydraulic separator (courtesy Sinus North America). Think of the output per unit of mechanical room floor area Each boiler can be independently serviced. Flexible piping connects each boiler to low manifold. (Boilers have integral circulators and check valves.)

12 High efficiency gas-fired boilers hybrid multiple boiler systems Condensing boiler operates during baseload conditions when water temperatures are lowest. 300,000 Btu/hr! mod/con boiler! (fixed lead stage) Conventional boilers are staged on when needed, and after water temperatures are above condensing mode operation 100,000 Btu/hr 100,000 Btu/hr conventional boilers for stages 2 and 3! (these boilers rotate in firing order) Heat output (Btu/hr) Heat output vs. supply water temperature! for panel radiator system stage 2 begins operation stage 3 begins operation heating load profile condensing range Supply water temperature (ºF)! (based on space temperature of 70 ºF) non-condensing! range stage 3 on continuously stage 2 on continuously condensing range approximate return water temperature (ºF)

13 Multiple mod/con boilers for high capacity domestic water heating 14 simultaneously operating showerheads + whirlpool tub = 1 master bathroom Do you suppose this is the only bathroom in this house?

14 Multiple mod/con boilers for high capacity domestic water heating This approach could supply 450,000 Btu/hr to sustain a 15 gallon per minute load at 110 ºF delivery temp. indefinitely, even without considering the hot water reserve in tank. At other times, the multiplemod/con boiler system can reduce to 5-10% of full capacity for space heating while still maintaining high efficiency. 150! kbtu/hr 150! kbtu/hr 150! kbtu/hr hydraulic! separator multiple! boiler! controller supply! temperature! sensor to / from! other loads Much better than a single large boiler serving both DHW and space heating loads. 450! kbtu/hr HIGH CAPACITY! indirect water heater (prioritized load)

15 Multiple mod/con boilers for high capacity domestic water heating No Bottlenecks! If youʼre planning a high capacity DHW system itʼs critically important not to create bottlenecks to heat transfer between the boilers and the domestic water. multiple! boiler! controller hydraulic! separator supply! temperature! sensor GENEROUSLY SIZED PIPING No FLOW bottlenecks No HEAT TRANSFER bottlenecks ADEQUATE CIRCULATOR P & T! relief! valve! PLENTY OF HX anti-scald rated! tempering valve! DHW out cold! water! supply

16 No Bottlenecks: When an indirect tank simply can t provide the necessary heat transfer, use a generously sized stainless steel flat plate heat exchanger with a standard storage tank.

17 Hydraulic Separation:

18 Hydraulic Separation: Think of two circulators, operating simultaneously in the same piping assembly, as rival bullies on the same playground. When 2 or more circulators are operating simultaneously in the same piping assembly, they try to interfere with each other. This interference is undesirable! To avoid this interference the circulators need to be hydraulically separated from each other. There are several ways to do this...

19 MODULE 5: Circulators Hydraulic Separation: What is COMMON PIPING? Itʼs the piping components shared by two or more circuits. common piping circulator 2 circuit 2 circuit 1 circulator 1 The degree to which two or more operating circulators interact with each other depends on the head loss of the common piping. The lower the head loss of the common piping the less the circulators will interfere with each other. When the head loss of the common piping is very low, there is hydraulic separation between the circuits.

20 MODULE 5: Circulators Hydraulic Separation: When the head loss of the common piping is very low, there is hydraulic separation between the circuits. Very little head loss occurs! in this portion of the circuits. circulator 2 circuit 2 circuit 1 circulator 1 common piping

21 Very little head loss occurs! in this portion of the circuits. circulator 2 circuit 2 circuit 1 head loss curve including! common piping (both circulators on) circulator 1 common piping circuit 1 Assume that circulator 1 is operating, but that circulator 2 is off. The lower (blue) system head loss curve in figure 2 applies to this situation. Next, assume circulator 2 is turned on, and circulator 1 continues to operate. The flow rate through the common piping increases, and so does the head loss across it. However, because of its spacious geometry, the increase in head loss across the common piping will be very slight. The system head loss curve that is now seen by circulator 1 has very slightly steepened. It is the upper, (green) curve shown in figure 2. head loss (feet of head) 0 0 circuit 1 head loss curve including! common piping (1 circulator on) pump curve! (circulator 1) flow rate VERY small decrease in! circuit 1 flow rate! when circuit 2 is on very small change in! head loss across! common piping! when both circuits are on The operating point of circuit 1 has moved very slightly to the left, and as a result, the flow rate through circuit 1 has decreased very slightly. flow rate in circuit 1 when BOTH circuits! are operating flow rate in circuit 1 when it is the only circuit operating

22 MODULE 5: Circulators Hydraulic Separation: Very little head loss occurs! in this portion of the circuits. circulator 2 circuit 2 circuit 1 circulator 1 common piping Imagine a hypothetical situation in which the head loss across the common piping was zero, even with both circuits operating. Because NO head loss occurs across the common piping, it would be impossible for either circulator to influence the other circulator. This would be perfect hydraulic separation. Design tip: perfect hydraulic separation is not required to ensure that the flow rates through independently operated circuits remain reasonably stable.

23 MODULE 5: Circulators Hydraulic Separation: common piping (with HIGH FLOW RESISTANCE) circulator 2 circuit 2 circuit 1 circulator 1 The higher the flow resistance of the common piping, the more each circulator will influence flow in the other circuit (e.g. the lower the hydraulic separation of the circuits). Design tip: Common piping with high flow resistance is NOT good:

24 High flow resistance common piping - something to avoid D 144!P = ( Head ) % ' & " $ # head added (feet) psi P at 0 flow pump curve! for small circulator flow rate (gpm) small circulator P=22 psi large circulator P=17psi backseated! flow check P= 10 psi ON ON P produced" by 0 flow = 4 psi P = 5 psi ON larger circulator ON smaller circulator P=12 psi P= 5 psi P=13 psi P=16 psi P=17 psi no flow common piping and! heat source have! HIGH FLOW RESISTANCE common piping and! heat source have! high flow resistance

25 MODULE 5: Circulators Hydraulic Separation: Conventional cast-iron boilers have very low flow resistance. Modern compact boilers have much higher flow resistance. space heating zones low flow resistance cast-iron boiler If a compact boiler is cut and soldered in place to replace a cast iron boiler, Interference between simultaneously operating circulators is likely. high flow resistance mod/con boiler space heating zones

26 MODULE 5: Circulators Hydraulic Separation: Divide & Conquer: From the standpoint of hydraulics, each circuit can be designed as if itʼs a stand-along circuit. circulator 2 circuit 2 circulator 2 circuit 1 circuit 2 common! piping common! piping circulator 1 circuit 1 common! piping circulator 1 Design tip: Hydraulic separation allows designers to think of an overall system as a collection of independent ( hydraulically isolated) circuits.

27 MODULE 5: Circulators Hydraulic Separation: Divide & Conquer: Simplifying system analysis Preventing flow interference

28 MODULE 5: Circulators Hydraulic Separation: Divide & Conquer: HW P&TRV This portion of system filled with 40% solution of inhibited propylene glycol manifold G! (garage) supply sensor P8 356 injection mixing controller! brazed plate SS! heat exchanger 3/4" copper 30 psi! PRV fill/purge P7 strap-on! aquastat! contacts! close at 100ºF! open at 50ºF panel radiator variable speed! pressure regulated! circulator! set for Pc 12D TRV TRV to / from other! radiators thermostatic radiator valves! on each panel radiator TRV TRV TRV TRV These panel radiators are representative! of second floor heating distribution system! exact size and number of panels may vary,! but all are supplied with 1/2" PEX-AL-PEX tubing, and controlled by individual thermstatic radiator valves. CW 12D 1.25" copper tank 1.25" copper acqustat swing! check 12D 2" air separator PRV LWCO MRHL P1 2" copper brass unions! (typical) 12D 3/4" copper P6 12D 1" copper 3/4" copper 3/4" fast fill piping 3/4" cold water supply 12- circuit manifold distribution system using PEX or PEX-AL-PEX tubing 2" copper balancing! valve balancing! valve! indirect water heater floor! drain cast-iron sectional boiler! with oil burner 12D 3/4" copper 12D In a complex system like this... return temperature! sensor for 356! mixing controllers 2" copper supply! and return headers! keep as short as possible all three injection pumps! equipped with internal! check valves 1" copper 3/4" copper 356 injection mixing controller closely spaced tees P2 1.25" copper 12D 1" copper purging! valves P3 outdoor! sensor! mix supply! sensor 1" copper 1" copper 3/4" copper 3/4" copper 3/4" copper 3/4" copper 3/4" copper 3/4" copper closely spaced tees P4 1.25" copper 12D 1" copper Webstone! purging! valves 3/4" copper P5 outdoor! sensor 356 injection mixing controller variable speed! pressure regulated! circulator! set for Pc! mix supply! sensor 1" copper zone valves 3/4" copper 3/4" copper 3/4" copper 3/4" copper How does the water know where to go??? manifold A manifold B manifold C manifold D manifold E manifold F manifold H (2nd floor) manifold I (2nd floor)

29 MODULE 5: Circulators Hydraulic Separation: P8 TRV TRV TRV TRV TRV TRV Divide & Conquer: P1 P7 P6 low flow resistance heat source! + short / fat headers Hydraulic separation allows designers to think of an overall system as a collection of independent ( hydraulically isolated) circuits. cast-iron sectional boiler P3 P2 P5 P4 In this system, hydraulic separation was achieved using short / fat header in combination with low flow resistance heat source. manifold H (2nd floor) manifold I (2nd floor)

30 Primary / Secondary piping - where it all began... Primary / secondary piping, using closely spaced tees, is now well known and often used in North America. flow-check valve secondary circuit Primary / secondary piping, is one way to achieve hydraulic separation between circulators secondary circulator primary circulator primary loop closely spaced tees flow D maximum 4xD But primary / secondary piping is not the ONLY way to create hydraulic separation...

31 Primary / secondary piping (one way to provide hydraulic separation) swing check (or flow-check) valve (on return) circulator with integral flow-check (on supply) spring-load check valve on supply circulator with integral flow-check! (on primary circuit) underslung thermal trap! (minimum 18" deep)! protects return circulator with! integral flow-check! (on supply) primary! circuit 18"! min. swing-check! on return circulator with integral flow-check! (on supply) this secondary circuit is lower than primary circuit This is a SERIES primary loop. It will create a sequential drop in water temperature from one secondary circuit to the next.

32 Primary / Secondary piping - where it all began... secondary circuit Primary / secondary piping, using closely spaced tees, is now well known and often used in North America. secondary! circuit load! #1 secondary! circuit load! #2 primary! circulator Primary / secondary piping, is one way to achieve hydraulic separation between circulators. But primary / secondary piping is not the ONLY way to create hydraulic separation... primary! circuit! (series) load! #3 secondary! circuit closely! spaced! tees! (typical)

33 Series and parallel primary/secondary systems secondary circuit SERIES primary loop secondary! circuit secondary! circuit PARALLEL primary loop load! #1 load! #2 load! #1 load! #2 load! #3 primary! circulator parallel! primary! circuit primary! circulator crossover! bridge primary! circuit! (series) closely! spaced! tees! (typical) closely! spaced! tees balancing valves load! #3 secondary! circuit Both series and parallel primary/secondary systems require a primary circulator. This adds to the installed cost of the system AND adds hundreds, even thousands of dollars in operating cost over a typical system life.

34 An example of primary loop circulator operating cost: Consider a system that supplies 500,000 Btu/hr at design load. Flow in the primary loop is 50 gpm with a corresponding head loss of 15 feet (6.35 psi pressure drop). Assume a wet rotor circulator with wire-to-water efficiency of 25 is used as the primary circulator. The input wattage to the circulator can be estimated as follows: W = f ΔP 0.25 = = 552watts Assuming this primary circulator runs for 3000 hours per year its first year operating cost would be: 1st year cost = 3000hr yr 552w 1kwhr whr $0.10 = $ kwhr

35 An example of primary loop circulator operating cost: Assuming electrical cost escalates at 4% per year the total operating cost over a 20-year design life is: c T = c 1 ( 1+ i ) N 1 i = $ ( ) 20 1 = $4,931 This, combined with eliminating the multi-hundred dollar installation cost of the primary circulator obviously results in significant savings.

36 Question: What is the ideal header in a hydronic system? Answer: One that splits up the flow without creating head loss Think about a copper basketball with pipes sticking out of it in all directions. very low head loss! inside header Wouldnʼt this be pretty close to an ideal header???

37 So why donʼt we build headers like this??? Instead, we approximate the ideal header by making it short & fat very low head loss! inside header Short / fat headers are GOOD! Long / skinny headers are BAD! short fat