Hydronics – Step by Step Heat Loss Example
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Hydronics – Step By Step Heat Loss Example • 10 x 15 room, 9’ ceilings 4x5 4x5 – Indoor design temp: 70 – Outdoor design temp: 0 – 2 outside walls (.018) 17’ 5x6 – No heat above or below – Window R-Value: 2.77 – R-19 in walls – R-38 in ceiling – R-19 in floor 15’ • Infiltration = L x W x H x DTD x Inf. fac. – 10 x 15 x 9 x .018 x 70 = 1701BTUH • Windows, walls, ceiling, floors = L x W x DTD x U Value – Windows: 60 x .36 x 70 = 1,512 BTUH – Wall: 165 x .05 x 70 = 578 BTUH – Ceiling 10 x 15 x .02 x 70 = 210 BTUH – Floor 10 x 15 x .05 x 70 = 525 BTUH – Total: 4,526 BTUH Boiler Sizing Terms • What’s the difference between DOE capacity and I-B-R Net Output? DOE is a federal rating and considers the boiler installed in a heated area and that all jacket and piping losses are usable and help offset the heating load. IBR considers the boiler to be installed in an unheated area, and that all jacket and piping losses are unusable. It is 15% lower than the DOE output rating. • What is “pickup” allowance? IBR calls for a pickup allowance that allows for the heating up of cold pipes and boiler sections – those have to be heated up first before heat can be delivered to the rooms. It’s included in the 15% de-rating of the DOE output. Point Of No Pressure Change • Where is the “point of no pressure change? It’s the point in the system where the expansion tank connects to the system – and is the 1 point in the system where the circulator cannot change the system pressure • What 3 things can change the system pressure at this point? 1. Add/remove water from the system 2. Add/remove air from the expansion tank 3. Increase system volume by heating up the water • What happens if the circulator is placed BEFORE the expansion tank? Circulator will show it’s pressure differential as a negative – system pressure will drop after the expansion tank – could cause noise or other air related issues. • After the expansion tank? Circulator’s pressure differential will show as a positive – keeping system pressurized and keeping air dissolved – quiet, efficient operation, longer circulator life, no air problems. Centrifugal Pump • Create a pressure differential in the system • High pressure goes to low pressure, thereby creating flow • Why is it a circulator and not a pump? It works in a closed loop system and unlike a well pump, doesn’t need to “lift” the water. How The Water Moves ________ ________ • Water enters through the eye of the impeller • How is velocity added? vanes slap water outward using centrifugal force • How does impeller thickness impact performance? Thicker the impeller, more flow circulator produces • How does impeller diameter impact performance? Wider the impeller, more pressure it produces. • How does speed impact performance? Faster the speed, more flow and pressure it produces • What’s the difference between open and closed vane impellers? Open vane impellers are for high flow, low head circulators; closed vane are for high head, low to medium flow circulators "Head" • What is “head loss?” Measure of pressure drop in a piping system • What produces head loss? Friction loss in the piping system creased by pipe, valves and fittings. • 1 PSI of pressure drop = 2.31 feet of head • Does height of the building influence head loss? No • Why? It’s a closed loop system. The circulators doesn’t need to push water to the top – same amount of water is coming back down the return Sizing A Circulator • Gotta do the MATH! • Must do a room by room heat loss analysis • Universal hydronics formula – GPM = BTUH ÷ΔΤ X 500 • Headloss – Zone length x 1.5 = total developed length – Multiplier accounts for fittings and valves – Developed length x 0.04 = head loss – Four feet of head for every 100 feet of pipe Let’s Do One… • Pipe sizing: – 2-4 GPM = ¾” M, 4-9 GPM =1’ M – 8-14 GPM = 1¼” M, 14-22 GPM = 1½” M • One baseboard zone – 27,000 BTUH load, 200 ΔT, 100% water 27,000 • GPM = GPM = 2.7 20 X 500 • Zone length: 80 feet – 80 x 1.5 = 120 feet total developed length – 120’ x 0.04 = 4.8 feet of head Pick A “00” Which one? Maybe a 006, more likely a 005 or most likely a 007.