The home heating oil industry has a long and proud history, and Fuel Oil News has been there supporting it since 1935. It is an industry that has faced many challenges during that time. In its 77th year, Fuel Oil News is doing more than just holding
Issue link: https://read.dmtmag.com/i/668638
44 MAY 2016 | FUEL OIL NEWS | www.fueloilnews.com BY GEORGE LANTHIER HVAC/ HYDRONICS I've been a great advocate of "two-stage" operation for a long time— as indicated by the date this article was first published: 1992. Now I have updated it for this issue of FON, because I still really think that a commercial burner with low-high operation is great (if you can't afford full modulation) and I'm still hoping to see more use of a two-stage residential oil burner before my career ends. With gas mod-cons (modulating-condensing) staging is insane with up to 26+ stages! I think the best in firing techniques is already here with the flame retention head oil burner and high-static oil burners are almost perfected to the same degree, so what else is there? We have already seen this industry try to lower NOx levels and raise CO 2 levels through gas re-circulating/blue-flame technology, but it's just too damn expensive with low fuel prices. I think trying to sell this industry on that again is going to be one hard sell! So where do we go from here? I had a European two-stage prototype oil burner in my own home and I can define this burner in one word: awesome! The burner was a Riello Mectron 5M/2 and ran for 24 years with no major service of any kind! Anyway, enough of talking about things you can't buy. What about something that you can buy and that is also old-hat to many of us, two-stage system operation. Many years ago, John Woodworth of the Hydronics Institute (I-B-R), published a technical paper that was reprinted in many magazines, including this one. It was all about the benefits of two-stage operation. It was titled "Controls for Zoned Hydronic Systems" and it was based on an I-B-R research project, which compared a hot-water heating system operated by three different control modes: outdoor reset controls; one-stage thermostats; and two-stage thermostats. The result of this testing was to find that the most efficient of the three types of control systems was the two-stage thermostat, which not only resulted in more efficient operation of the burner but also better utilization of the equipment. Now many of you may be wondering, "What the hell is a two-stage thermostat?" Well, it's really better known by its alias, a heat-pump thermostat. What it really is, is two thermostats in one box. Let me tell you a few dif- ferent ways that I have put it to work over the years in all kinds of systems. After reading John's article you see, I was so charged up I went out and tried sticking these things on everything. Here are some of the results. First of all, my previous home, Figure 1. What you are looking at here is a wiring diagram for a four-zone system with zone valves which provide for two-stage operation. The thermostat's first-stage turns on the zone circulator and starts to pump the water out of the boiler. If there is hot water in the boiler, a "purge-down" effect takes place. If the water is hot enough, the zone may be heated from the burner's last firing cycle. But, let's say that the boiler is cold at 100°F (warm-start). Well then, the temperature at the thermostat contin- ues to drop and now the burner fires. Here comes the great part. The temperature at the thermostat starts to rise so that the thermostat's second-stage becomes satisfied, which means the burner is shut off. The zone circulator, however, continues to operate, and brings those valuable little Btus out of the boiler until the first-stage is satisfied and then the circulator goes off. Holy cow, just imagine what hap- pens to stand-by losses on this system! Remember, if you don't use those Btus that you pulled out of your fuel, they're wasted! "Oh yeah, what about your two-stage burner, George?" The house is heated by a four section boiler and that only went to high-fire (0.90 gph), if the outside temperature goes below 22°F. otherwise it stays in low-fire (0.65 gph). The staging occurs through the use of an outside thermostat. Pretty slick, huh? As you can see, two-stage thermostat operation requires the least technol- ogy to get some really great results. No fancy panels, computers, black-boxes or voodoo here. Now, what about a warm air job? Well, you could use this prin- ciple with multiple furnaces. Let's say that you have a big house with an obsolete larger furnace, like one of those old American- Standard Sunbeam Models at about 250,000 Btus, Figure 2. You could put in a new commercial furnace that will have a commercial high-speed burner, but I would also suggest earplugs, and watch out for those blower speeds too! Another option would be to put in two residential units under the common ductwork and step-fire them with that two-stage thermostat again. The blowers would Two-Stage Burner High-fire Burner & Low-fire High Limit DHW Circulator HEAT Circulator Flow Switch Outdoor Thermostat Zone Valve Zone Valve Zone Valve Zone Valve Zone Transformer Thermostat Thermostat Thermostat Thermostat R1 = SPST R2 = SPDT R2 2 1 3 4no 4nc 2 1 3 4 BOILER TANK DHW AQUASTATS R1 Service Switch Thermal Switch Customer Switch L1 L2 Fuse Box T T 3 2 1 3 2 1 3 2 1 3 2 1 Figure 1