Image Credit: Christopher Clapp/Fine Homebuilding magazine
More Q&A Spotlight
Matt Cooper的1,800平方英尺的木工店铺坐落在一个带有辐射楼层系统的6英寸混凝土板上。遗憾的是，Cooper用于加热用于板式管道的水的按需热水器并不表现良好。
“我一直在使用一个Takagi Jr.to heat it for the past couple of years but it’s been no end of headaches,” Cooper writesin a Q&A postat Green Building Advisor.
“I’d like to figure out a better way to heat the water,” he says, “probably a direct-vent system so that the wood dust doesn’t create problems with the burner (just one part of the TK Jr. issues). It seems that my options are either a better version of the current on-demand hot water heater/boiler, or a tank-style water heater.”
The building and the slab seem to be well insulated, but Cooper’s hot-water options are limited to propane (at $2.25 per gal.) and electricity (12 cents a kWh).
Cooper’s options are the topic for this Q&A Spotlight. (Neil B. posteda similar questionabout heating a workshop elsewhere on the Q&A Forum.)
罐式加热器简单可靠
A.J. Builder recommends a tank-style water heater for Cooper’s system. “Tank units rarely have issues,” he writes. “Simple installs available from manufacturer.” He says he’s dealt with similar heating systems for decades, and would recommend installing the water heater in a dust-free utility closet.
“Standard tank units are bullet- and idiot-proof,” Builder writes. “I just installed an[A.O.] Smith 50向客户,花费1000美元。PVC发泄和intake. Four hours — done.”
Other suggestions from A.J. Builder include turning down the thermostat, burning wood pellets if he needs a cheaper fuel, or raising his prices.
Woodworking shops are…
9 Comments
太阳能盒
pre-heat the water through a black solar box and black coils placed in direct sunlight.
你在哪里得到这个例证？
We are required to put continuous R-10 under our heated slabs, and I've never seen anyone sculpt their gravel base with that nifty transition from 1" to 2" insulation thickness. The welded wire fabric looks good where it's drawn, but I've always seen it laying flat on the ground, never up on chairs or other supports, so you're depending on the slab finishers to somehow pull it up to mid-slab as they walk on it (yes, I know, some concrete rakes have a little nub on them specifically for pulling the mesh up). I prefer #4 rebar on 1-1/2" dobies. And I guess Martin didn't get his way on this one, with the vapor barrier under the insulation.
Response to David Meiland
大卫，
Scott chose to illustrate this Q&A Spotlight with an old illustration from Fine Homebuilding. You are quite right to point out that the illustration is showing its age.
We can't afford to draw up a new detail every time we publish an article, unfortunately. Your points are valid; thanks for making them.
30,000 BTU/hr,not 23,600 BTU/hr: Real designs need real math.
0.62的EF并不意味着它会在空间加热应用程序中获得62％的效率。
当用于加热空间加热时，燃烧器的占空比比在EF测试中占据63奇的加热水的数量级。非冷凝罐加热器的稳态热效率（100％占空比）约为80％，而不是62％，并且在空间加热型循环中，您将非常接近稳定状态，而且肯定没有不到78％。
The difference in the stated output number is more than 25% bigger, which is a big enough difference that it really needs to be factored into any real system design.
The financial math chucking a system that can be re-commissioned to function optimally for something like ~$500 don't favor buying a new tank heater, condensing or otherwise.
Designing a radiant slab heating system around a non-condensing tank HW has some real issues to be considered too, if you want the thing to last. A water heater like that is NOT designed to be operated at continuous flow with the low-low return water temperatures you will get from a radiant slab. Under those conditions the heat exchanger sees copious levels of destructive condensation, severely shortening it's life. While that's fixable with radiation bypass plumbing or other standard hydronic designer tricks of the trade, it's absolutely essential to get it right, or you'll be back at square one in short years. For those unwilling/unable to do the math and design enough hooks into the plumbing to protect it, and do the requisite system measuring/tweaking/commissioning, the State GS6-40-HBDS or similar would be a TERRIBLE choice for a slab radiant system.
Finned copper water tube heat exchangers like that of the Takagi Jr. are much more tolerant of continuous low temp incoming water, which is why most swimming pool heaters use that type of heat exchanger, and why purveyors of one-size-fits-all slab radiant heating systems go that route. If only they didn't abuse it in other ways it works out just fine, which is why simply fixing the deficiencies of the current system is probably the right way to go.
当然，冷凝热水器（如顶点），从返回水温度的凝结下来的冷凝器中获得了效率，利用将损坏非冷凝罐的因素。这使得潮湿 - 黑客设计师更好/更安全的选择，而是与修复Takagi-JR相比的大块变化。基于系统。
Reply to Dana Dorsett
我当然不能对你呼叫我的潮流黑客设计师来竞争。我一直在滋补这些系统，几十年作为水管工和建设者，但我不是工程师。我确实想知道你的表征以这种方式使用的坦克作为连续占空比或低低的返回温度。
I have several of the direct vent state water heaters I mentioned out there still heating floors and producing domestic hot water after fifteen years or more. The return water is generally around 70 degrees and it is being mixed with the return water from the floor loop to supply 90 degree water to the floor so the flow rate is generally very low and the duty cycle is not continuous in that the the flame is not burning more than once every twenty minutes or so in the relatively low energy use passive solar homes they are installed in here in North Carolina. Of course It would be a different story if a system like this was used for driveway snow melt or for heating a large and drafty building.
During the DOE combined heat and hot water meeting at the2010韦斯特福德研讨会，来自自然资源的马丁托马斯加拿大概述了许多他们试图迫使无水加热器加热器的问题。为空间加热服务。一些讨论中的一些录制了低至50％的服务效率，并且我在换热器中看到了过多的烟灰累积，延长了低燃烧率。
I guess another approach rather than suggest a different water heating device would be to ask what is causing the trouble with the existing tankless unit. How would you propose to spend $500 to fix the problem he is currently having with making his tankless unit play nice with his radiant floor?
It's still a real hydronic design problem.
There are plenty of hydronic hacker hobbiests out there- you can count me among their number.
我只完成了一个基于无油桶HW加热器的一个组合加热系统，但在2008年委托它的情况下，它一直在毫无问题地运作。它仍然击中它的原料燃烧效率数，并且已经存在零问题 - 到目前为止唯一的维护清洁过滤器。它不加热一块板 - 它是一种多/微调系统，具有不同于电镀的子地层辐射到铸铁RAD的辐射，所有设置为液压卷材，全部设立在125-130F水温下运行。无罐在48加仑的缓冲罐上设置为130F的水管，并从罐中啜饮所有辐射。虽然在缓冲罐内的热交换器绘制了国内热水。如果添加了一个板坯区域，它需要一个搅拌器阀门，但它不会改变储烟的操作特性，该装置与〜2gpm流量和158个输出设置，所以它会调制〜75k btu /HR当坦克底部的返回水滴时用多个区域呼唤大热水时呼唤热量，但在〜28kbtu /人小时内完成了缓冲区上的Aquastat的〜28kBtu / hr，这是关于它的1/5点射击范围。在该地方的设计热负荷约为36-38K，空气处理器线圈本身将超过40K，但它们从未耗尽热水或热量。这是kludgy，但它的工作原理，并且是专为特定负载和辐射而设计的。 A condensing Vertex would have been cheaper/easier, but would have had capacity issues under the highest concurrent loads. It was a much messier design problem than space-heating only on a single-zone slab, but it allowed micro-zoning the system without short cycling the thing into an early grave.
Pumping rates matter on the non-condensing tanks too. At sufficiently low pumping volumes you can get there direct-pumping the water heater without ending up destroying the heat exchanger with condensation. It's best to actually design it, but sometimes dumb luck gets you there too- if it works, don't change it. If it's only doing 3 burns an hour at a 10-60% duty cycle that's a lot more ignition cycles than the equipment was designed for, but that's also comparatively cheap to fix should the ignition components fail. But there are numerous examples of folks in New England where counting on dumb-luck on non-condensing tank based slab-heating systems hasn't worked out so well, usually a function of pumping rates and duty cycles that are too high resulting in condensation problems.
With Matt Cooper's existing tankless system if the pumping rates and delta-Ts are at all reasonable he may be able to just install the $55 direct-vent kit and some cheap tin duct to bring in the combustion air and call it done for under $100. But it may need tweaking to run optimally. If optimizing his system involves installing different pumps it might end up closer to $500, but probably not more than that. Without knowing the full extent of what's there it's hard to say, but simply yarding out the tankless and plumbing a tank in it's stead without doing any sort of design assessment/adjustment would be risky.
We don't really know what sins of omission/commission are on his system. Most of the internet vendor systems are plumbed primary/secondary with separate pumps and more often than not over-pumped on the tankless loop resulting in a low a delta-T on the tankless and a relatively (and unnecessarily) high-fire on the burner, and almost never set up to modulate with load. Some are pumped direct into god-knows-what amount of pumping head to the radiation with fingers crossed- there are all sorts of hacks out there that should never have been offered as a product for sale that kinda-work, but not optimally.
Doing a sort of real heat load calculation is the first part, then setting up the flows on both the primary and secondary loops so that the tankless delivers the design condition amount of heat at delta-T of between 25-75F at a flow of 2-3gmp on the tankless end is generally pretty nice to the tankless, and even if it only modulates within a narrow range, matching the output to the actual peak loads will result in fewer ignition cycles.
Forgot to mention...
。。。an 1800' shop building located near Ithaca NY where the 99% outside design temp is 0F could easily have a heat load in excess of the ~30,000 BTU/hr full burner output of State GS6-40-HBDS direct vented non-condensing hot water heater.
但热负荷不太可能是TK-JR的全输出的一半。
Design temps for NC are 15-25F warmer than that, and heat loads of houses designed for passive solar are probably going to be well under those of a code-min or even better-than-code shop building in upstate NY. The right solution for one is unlikely to have a close resemblance to the right solution for the other.
I'm guessing the peak heat loads of the NC solar homes are under 15K (half the full output of the State water heater), which means the flow & turbulence inside the tank less- under under 1gpm of flow in the tank at 50F delta-T between return water & setpoint. That very low flow /low turbulence delivers a lower risk of condensation than when trying to pull the full 30K out of it, which CAN be done, but at more than 1gpm, which delivers a lot more turbulence (= higher condensation risk.) With near-tank bypass to keep the return water above 120F, and setting the tank to 140F or even higher you can get there without destroying it, but it's a more complicated design.
Tankless to Air Handler Combination
BSC's research (headed up by Armin Rudd) has primarily looked at connecting a tankless water heater to a fancoil (air handler) forced air system. He added a small storage tank as a buffer, which should reduce short cycling issues. Not sure if it is the right solution here, but I thought I'd bring it in to the discussion. RR-1206: Measure Guideline–Combination Forced-Air Space and Tankless Domestic Hot Water Heating Systemshttp://www.buildingscience.com/documents/reports/rr-1206-measure-guideline-combination-forced-air-space-tankless-domestic-hot-water-heating-systems/view?searchterm=tankless。John Siegenthaler推动使用带低质量冷凝锅炉的缓冲罐，当连接到低负载房屋时，以解决短暂的循环问题 - 例如，在2011年JLC制品用于低负载房屋的水性水力加热中http://www.jlconline.com/hvac/hydronic-heating-for-low-load-houses.aspx.
Response to Kohta Ueno
BSC研究中的缓冲罐应该只需要降低国内热水的短期，并在水龙头处提供更均匀的水温。它看起来他们用Taco-009过度抽水，好像它是一些真正的高头循环。（我想在那个上看到他们的数学！）使用空气处理程序，作为唯一不必要的热发射器。通过辐射板坯，板坯的热质量比10加仑缓冲液中的〜85磅水的热质量增加了10个倍。只有低输出低质量辐射或微调中部质量系统将导致空间加热端短循环。
该设置的Gunk /堵塞和腐蚀问题是由于它们在辐射中运行饮用水而不是将其运行为封闭系统。在Matt Cooper的加热闭环应用中没有发生，或者在坦克的klude，因为它只是在封闭系统中才能在封闭系统中运行“死”加热系统水，但每天没有新的野人或氧气进入系统。在封闭系统中，不需要昂贵的青铜或不锈钢泵。
Siegenthaler的做法有点过分了——它的much cheaper to do the same thing using a plate heat exchanger isolated heating system using a condensing hot water heater as the buffering mass as well as the potable hot water source. But since it requires two pump you'd be at 100-120watts of pumping power rather than his 30w ECM drive pump. But at the duty cycles it's running on low-load house it's hard to rationalize the additional cost of the pumps just so save 100kwh/year. At the current cost of rooftop photovoltaic solar making up the difference in power use with a partial-panel of PV is cheaper than the single ECM drive pumped system. Yes, the high mass Versa Hydro with an ECM pumped system is a marvel of efficiency, but there's some cost-optimization that could be factored in too. For a small hit in efficiency you can get there with a Polaris or Vertex. He finishes with:
“还有许多其他的系统配置that would be suitable for low-load houses. Most of them will embody several of the desirable characteristics described earlier. The goal in designing any of these systems is to leverage the inherent advantages of the newest technology while keeping the system as simple as possible."
TESTIFY, brother Siggy!
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