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Hot Water Heating Zoning strategies for hydronic systems By Roy Collver It is frustrating to deal with a customer who compares the cost of a hydronic heating system to the usual off-the-shelf forced air system that many builders offer as a standard. The builder usually offers only a fraction of the true cost of the forced air system as a credit and whacks a big mark-up onto his quoted price for a hydronic system. To add even more pain, the customer often opts for a system that treats just about every room as a separate zone, forgetting that the forced air system was designed with a single thermostat and treated the whole house as one zone. Every time you add a zone to a heating system, you add hundreds of dollars in cost. The good news with a hydronic system is that zoning is relatively inexpensive compared to a forced air system. Let’s look at how to go about zoning hydronic heating systems and come up with some easy rules to get your customer the most bang for the buck. There are three ways to control the heat output from the terminal units: 1) We can start and stop the flow of heating fluid. 2) We can speed up or slow down (modulate) the flow of heating fluid. 3) We can leave the flow constant and adjust the fluid temperature to give us more or less heat. Modulate the flow The first method is accomplished by using an on/off zone valve or pump controlled by a room temperature thermostat. The heat terminal units alternately heat up and cool off, pulsing the heat into the room. This is probably the most common method used in North America today. It is relatively inexpensive and offers customers a wide variety of choices when it comes to thermostats – from simple mechanical wall thermostats to electronic, multi-schedule, programmable set-back thermostats. The most complex systems use room sensors, feeding back to a building management system that can be accessed from a remote location for monitoring and adjustment. The building management system in turn operates the zone valve or pumps. Thermostatic valves The second method is normally accomplished using thermostatic radiator valves. These have an internal device that throttles fluid flow through the terminal unit (radiator, radiant floor, etc.), increasing the temperature drop through the terminal unit and changing its average temperature. The throttling device is actuated by a thermostatic head either mounted directly onto the valve or, by using a capillary, mounted remotely on the wall. This method, hugely popular in Europe, is the least expensive and simplest way to zone. It is becoming more popular here, but its biggest disadvantage is that room temperature setback has to be done through a central system setback (lower the water temperature in the whole system), or manually by turning down individual zones one at a time. Temperature adjustment The third method is technically the most correct way to do it. By changing the fluid temperature as required by the heat loss of the zone, but leaving the flow constant, the temperature drop across the terminal unit will be more constant and, theoretically, the room The good news with a hydronic system is that zoning is relatively inexpensive … temperature will be more even. Unfortunately, to do this properly requires a mixing system for each zone as well as some kind of room temperature feedback sensor, which gets expensive using today’s technology. A number of manufacturers are working on more economical ways to accomplish this. So now to the rules: 1) If your customer wants to zone every room and doesn’t mind paying for it – give them what they want. Ask questions about how involved they want to be in the operation of their system. Some well-heeled patrons may want a fullblown building management system so they can check on their house when they are vacationing in the Riviera. Or they may want the same system so YOU can monitor it for them. OR they may want simple thermostatic radiator valves – turn clockwise for warmer, counterclockwise for cooler. It is important to know the choices so you can properly explain them. 2) If your customer is worried mostly about the cost, look at the zoning possibilities and do some cutting. What zoning options can they do without? In some cases, they may be happy with a single thermostat, but explain what they will be giving up, such as: a) Sunny side of the house versus A zoned system can be simple or complicated. Careful communication with the customer is a must to determine their needs. shady/windy side: Rooms with large windows should be treated as separate zones. When the sun shines, the solar gain will overheat them and you will want to shut down or reduce the heat input from the hydronic system. (If the solar gain is extreme, these rooms may still overheat.) These windows will suck heat out of the zone on a cold windy night, but you can boost the heat input with a zoned system. b) Determine always-used rooms versus seldom-used rooms. Why heat a guest room, garage or unfinished basement to the same temperature as the rest of the home? High energy costs may dictate zoning choices. c) Special needs rooms: if Auntie Emma needs her room hotter than everyone else – indulge her. It is easy with a hydronic system. If your customer likes their master bedroom cooler – we can do that too. d) Special reasons. There are a myriad of special reasons to zone individual areas of a house. Some owners want their radiant floor warmed even in the summer. We can do that by using a floor sensor and treating the floor as its own zone. Once again, you MUST communicate clearly with your customer. I hope you aren’t getting tired of this message that I keep preaching, because I am not going to stop. Poor communication with the customer is the most common reason for dissatisfaction with hydronic heating systems. If you or your customer just cannot decide on whether to zone a particular area, make sure the distribution piping is done so that a zone valve or pump can be easily added later if necessary. Install a basement bathroom without breaking the floor. BEFORE AFTER (or the bank) • You decide where to put a toilet or bathroom, it is not dictated by the drainage situation. • Easy installation, do it yourself. • Your floors stay intact. No breaking, no mess. • 3/4” discharge pipe, which can be run virtually anywhere. • Over three million sold. • Clean, reliable, and virtually maintenance free. Add convenience • Add luxury • Add value to your home For a FREE brochure please call: 1•800•363•5874 To see the entire family of Saniflo products visit: www.saniflo.com Circle Number 115 for More Information www.plumbingandhvac.ca November/December 2005 – <strong>Plumbing</strong> & <strong>HVAC</strong> Product News 15
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