Joined on December 28, 2006
Last Post on May 19, 2011
@ May 8, 2011 1:33 PM in Before and After- 1913 Gravity System Re-PipeMikey asked me to post some pictures of my heating system re-work. My Susan and I bought this 1913 American 4-square last summer, finally consolidating our respective pre-marital homes into one.
Naturally, this was a cause for celebration in the form of not being satisfied with the heating system and setting about to re-work it. :)
The boiler is a 1990's W-M Gold Series at 100 MBH input. Attached were (3) 007's to very low head-loss zones, (2) baseboard and (1) gravity iron circuits. Given the low head losses and measured temperature rises, the boiler had over 42 gpm water flow through it when all zones were calling. It took 45 minutes to get nearly any appreciable heat to the house when fired. Could not have been a good thing. Further, the 80 gallon system volume was served by a single #30 expansion tank. The basement was auspiciously dry when we closed in late July and I wondered about the dehumidifier. When the system did get to temperature, thar she blows! Need more tank.
The largest piping is 3" and splits into 2.5" and 2". It had been converted years ago I am sure. This boiler was probably the third one, my guess. Last one was oil-fired.
The budget did not permit a change-out to a mod-con, so I set about re-working the system as will be posted. Here are "before shots".
@ May 8, 2011 12:51 PM in heat loss softwarethat your pipe sizing as roughed MAY be perfectly fine for a larger heat loss than you are thinking. I work near Downtown Crossing so if you want me to take a look as a courtesy, write me off-line and I will see what I can do. No obligation, just another pair of eyes. I am actually in the office today if you are around.
@ May 8, 2011 12:19 PM in New Boiler - Steel or copper pipes?I think I will, probably start a new thread. Everyone likes pictures... :) I appreciate the suggestion!
@ May 8, 2011 12:15 PM in This is Funnier than heck, Sunday funnieswet my pants... that was GREAT! Worth sharing with Susan and the kids.
@ May 8, 2011 12:10 PM in One foot in each century - please adviseLove reading happy outcomes like this. The Simple Wow Factor at work. Good on you both, Jamie and Ray.
@ May 8, 2011 12:02 PM in heat loss softwareFor the room you described, I get a net heat loss (no safety factors) of 6,468 BTUH, just under 36 BTUH/SF.
24SF glass x 1.13 x 70 = 1,898
96 SF net wall x 0.3 x 70= 2,016
180 SF roof x 0.04 x 70 = 508
Sub-total for transmission alone, no infiltration, I get 4,418 BTUH
I took infiltration at 1.0 ACH which comes to 27 cfm or 2,050 BTUH. Total 6,468.
Now, the reason my numbers may be higher than yours is that when measuring the exterior wall, I add for the structure above, the exterior wall within the structural thickness. In any building you have to account for that or you miss broad stripes of wall. So instead of 9' high walls, I used 10', then subtracted the glass area.
I think the lesson here is to have in your head some decent check figures. You KNOW that 16 BTUH per SF is too light. As stated and demonstrated above, 30 to 40 may be more in-line. Not a calculation method but just a sanity check.
As for the roughing in, do not despair especially if you are talking radiators. 1/2" PEX or copper can easily carry 7,500 to 10,000 BTUH as one example.
@ May 8, 2011 9:58 AM in Heat Loss CalculationRegarding daily temperature swings and your ability to withstand them: If your building enclosure is insulated, tight and forgiving (a lower outdoor temperature balance point, specifically), you can withstand a DHW call better than a loose house. (Seems obvious and it is.)
See, a sudden drop in outside temperature will not show up immediately inside, not for at least one hour (in an unimproved older house absent holes in the walls), and five hours to overnight in a tighter house. That is your floatation device.
If your home mass, even if wood frame, but being warmed, also acts as a thermal battery. Add to that, if the house is "at temperature or near temperature" and not "recovering from a deep set-back", you are also in a better position to negotiate with physics. :)
The slow pulsing of heat to maintain temperature at the rate it is lost (meaning good anticipatory control) is an asset you should have.
From what is being discussed here, my inclination falls in three camps, each of which will require you to think about how you live and work with each set-up.
Camp A says that you should get a separate source of DHW and let heating be "pure and tightly sized" -a 50 to 60 MBH boiler with a 5:1 turn-down. Let your DHW be a tankless type with a separate storage tank to be charged from it- abundant generation and volume to draw upon between charging periods. You may ALSO integrate an indirect in this as a back-up/assist or for summer loads, not to complicate things, but as an option. (The storage tank can also be an electric DHW heater. Hook up the elements if you need the boost but it is hard to beat the cost of these as an insulated tank. More on this later.)
Camp B says that you want to be more cost conscious and get as much benefit per dollar as you can. (Nothing ever wrong with that! But in this case you have a budget to adhere to.). To achieve that, I would say you go with a compromise 80 MBH boiler, maybe a 90-92 such as the Vitodens. Set up your DHW to charge in the AM before you warm up the house. Take advantage of "no heating demand" and be ready for AM showers while the house by then is warming up. With this setup, you lose the finer turn-down (your minimum if 80 MBH will be 16 MBH with a 5:1 turn-down, still not too bad). But if you need to top off your DHW on the coldest day, it will take maybe 30-40 minutes from a cold tank (unlikely), but 10 minutes during a shower.
A word on generating capacity relative to a shower: If you have low flow shower heads of 2.5 to 3.0 gpm (high by today's standards, but just for discussion), you will draw 2.0 gpm of hot water from the tank. To heat that steady state and keep up with it, will require between 40 and 45 MBH input at the boiler, roughly half the capacity we are talking about. What this means is that you can still charge the tank while taking a shower when all of the boiler capacity is being delivered. Not a bad place to be. Could you do this with a 60 MBH or 50 MBH boiler? Maybe, just less assurance.
Camp C is similar to Camp B, except you would favor a smaller boiler (50-60 MBH) and add a buffer tank or tanks, (thermal storage) to the heating side to carry you over the heating troughs when DHW is calling on the coldest day or the system is topping off the DHW. As a sub-option, you could also tie in an electric DHW heater both for storage and to trim those few high demand hours. Can be economical in the long run.
To the question, "does the boiler go out of condensing mode during DHW generation"?
Yes, for a time. If a cold tank start (really only once when you think about it!), your boiler water enters fairly cool because it too is just starting. It hits room temperature or colder tank water via the heat exchanger and returns to the boiler somewhere near the temperature of a Wiccan's mammary. Condensation reigns.
As the tank warms up as does the boiler, the boiler water being supplied crosses over the tank temperature and runs to limit (maybe 160-170, varies) or until the tank is satisfied, whichever comes first. During this time, yes, the return water may come back below the gas dewpoint (return water at or about 122F). But then it will continue to rise above condensing as the temperatures of tank and boiler begin to narrow. This phase does not last that long. Remember we are talking a 10-20 minute burn most times with the last half maybe being above condensing. Not a huge loss really.
As for radiant design, yes, I would start a new thread. There is a glaze-over point especially where the focus goes astray and you may miss responses you desire. My take anyway!
@ May 7, 2011 5:03 PM in Heat Pump Water Heater in Mechanical RoomIf it is a warm and even humid room otherwise, there is a product, name escapes me. This device is an AC unit/dehumidifier which sits atop the DHW heater and uses the hot gas waste heat from the refrigerant process to pre-heat the DHW incoming cold water. (Rather uses the incoming CW as a water-cooled condensing medium).
If I come across the name I will post it but others I am sure know the one I am talking about.
There also were a line of Free-heaters from Spiro (the spirovent people) and Meuller refrigeration specialties, to take the same hot gas waste heat from commercial refrigeration and use it also to pre-heat incoming CW to DHW systems. We specify the Meuller line on commercial kitchens but I see no reason it cannot be adapted to other AC processes.
Depending on how hot the room is, a more passive coil situation could be used, but the refrigerant boost is more positive.
How hot IS this room? It may be as hot as my grandfather used to say: "Hot as a June Bride in a Feather-Bed". Now that, my friend, is hot. :)
@ May 7, 2011 4:54 PM in uneven air controlon how open or how isolated the spaces are from one-another. Not to mention the temperature differences maintained. If one area really is 55F and the other is 72, that has to be two very isolated spaces/portions of the house!
The actual effect you describe depends on the proportions of course. Half the air at 55F and half at 72F means that the furnace or coils will see 63.5F air. Good for the cool side, a bit of a climb for the warm side. Your active zone coil output (if hydronic), will increase somewhat to meet this due to higher delta-T on the air (and water), to a point.
I think you are thinking about it correctly but maybe over-thinking it a bit too. For example, in about 95% of my designs, we have VAV boxes on supply only. (Granted we do not have a wide range of temperatures to be maintained; the systems strive for the same temperature versus variable loads such as sun in some rooms, computers in the other.)
But the other 5% would be medical facilities and laboratories where pressure relationships rule. A sudden heat load in a lab forces in more supply air yet the lab may have to be negative pressure to its neighbors, so we provide an individual interlocked air valve on the return/exhaust side.
To do that on a house with otherwise reasonable return air paths? I would have to come up with a reason to justify doing so, adding expense and complexity. Not saying it is not advisable, I just cannot think of a rationale for doing this in a house as I presume you are discussing.
@ May 7, 2011 4:43 PM in heat loss software30 per SF is more in line as a check figure than 16.
I recently did an assist/check calculations for a small radiant job on Beacon Hill. The space was a walk-out basement, so partially below grade. The radiant at 30 was not enough for design days so was supplemented with some of the existing cast iron radiation.
If your spaces are above-grade and amortize that heat loss over more SF, 30 seems reasonable, but on a specific room basis (more exposed wall and glass and net room SF not counting interior hallways, etc.), you may well find yourself above 40 BTUH per SF in my experience.
We know you cannot insulate and storm windows are only allowed on the interior so air sealing is your friend, the only tool you really have. So we admit defeat and have higher BTUH per SF check figures than your supply house has. I suspect they made assumptions of insulation values being rational. Can you check their inputs? They may also have used incorrect SF numbers as a divisor, who knows? But it is off significantly in my experience too.
If you like, bounce them by me for a sanity check.
@ May 7, 2011 4:33 PM in snow meltare recommended when opening your electric bill :)
Seriously, depending on your local utility costs, electricity tends to be 1.5 to 3.0 times the cost of fossil fuel.
First off, in my first response (and not knowing where the installation is), I had meant to comment on your BTU density and the ability of the system to support that with other things going on. The BTU density could be 100 to 300 per SF also depending on the confidence level of how reliably clear they want the panel to be.
In your case, say your 200 SF panel requires 200 BTUH per SF or 40 MBH total. Electrically that is 11.72 call it 12 kW to operate.
With gas at 90% efficiency, that 40 MBH output will require 0.444 therms per hour.
If your costs locally reflect ours, (18 cents per kWH and $1.85 per therm gas), your hourly costs would be $2.16 electric and $0.82 for gas, a factor of 2.62 for electric over gas.
If each snow cycle, say an hour before and for 12 hours total, your "cost per storm" would be nearly $26 for electricity and $9.84, call it $10 for gas.
How many storms in your area? If say ten per year, the math is easier. In the scheme of things, it seems about in line with hiring a local kid who does excellent work including good edges. :)
@ May 7, 2011 2:48 PM in snow meltOperating cost differences aside, electric mats can and do burn out and not in a way you can repair such as a leak with hydronic.
The only maintenance I can think of is testing your glycol and adding inhibitor so it does not become acidic. Properly designed, controlled and isolated with a brazed plate heat exchanger, you can keep the water temperatures lower than your boiler enough so that the tendency to break down the glycol from over-heating is greatly reduced.
I would go with hydronic. Also, of the snow melt area is in the sun, it can be leveraged as a form of solar collector, good to keep the glycol moving and not stagnating where it gets bored and goes to mischief. :)
@ May 7, 2011 2:38 PM in New Boiler - Steel or copper pipes?My house was built in 1913 and has at its core a gravity HW system starting at 3" pipe and predominantly 2" and 2.5" pipe in each direction. Massive stuff held up with wrought iron staple brackets. I imagine the dead man who installed it had wrists the size of bricks and hands the size of eggplants. By hand with no Ridgid 1224 either!
Real men indeed.
@ May 7, 2011 2:26 PM in Heat Loss CalculationThat said, you are finding out as many of us do, that your typical boiler, even a ModCon, is too large for the average house! Putting in a TT 110 with an output of say 99 MBH will be nearly double the size it needs to be on the coldest day.
Speaking of heating alone, your heat loss numbers have climbed a bit in actual use. Now, that could be reflected in your having a higher Cd factor (maybe 0.75 in reality?), a lower system efficiency (65%? I do not know), or both!
OR, it could mean that your house has more air leakage, infiltration, than you have estimated. The conduction portion ("A * u * Delta-T") is fairly linear and "stable". Unless you have a blower door test or tracer gas test (blower doors being much more common and available), you will not really know. More to the point, a blower door test can reveal some "cheap wow!" air leaks. I have found old drain spout fittings disconnected, open chases from basement to attic, missing stones in a crawlspace, things that were fixed in four hours and yielded immediate -and measurable- improvement.
So why am I prattling on like this?
Because by testing and air sealing you MAY be in line to drop your heat loss by enough to allow use of the nice SMALLER boilers, a Lochinvar Knight 80 or even a 50, or a TT 60 or 80 (I think they have an 80). Ideal for heating only, tightly sized to the house heat loss and modulation tailored to the heat loss of the moment. How cool.
Issue Remaining: Domestic Hot Water Production:
It may be a longer haul to heat domestic water with a smaller mod-con. It is common practice NOT to add capacity for DHW production, especially when you have a 90 to 110 MBH input boiler and your heat loss is in the 40-60 MBH range.
See, you always had plenty of reserve even on the coldest day, for DHW production.This was because there were few if any smaller boilers in the US market. Now that you have the 50-60 MBH input range, you can heat with high efficiency and modulate down as you need to, as a heating-only device.
When you had a roughly 100 MBH input boiler, that all went to heating your tank in 20 minutes or less without your heat feeling a blip. This is three times the pick-up of a conventional tank type heater (33-35 MBH in a 40 gallon tank).
So now, if you have a 50-60 MBH boiler, it may take 40 minutes to heat that tank and it will not be heating your house during that time.
So by this I am asking if you might think of a separate means to generate domestic hot water and get a smaller boiler which will modulate down to 33% (or with a Lochinvar Knight, 20%) and enjoy your ideal heating efficiency.
@ May 6, 2011 10:05 PM in Heat Loss CalculationMy solar point was over-stated and ill-advised given your location!
Agreed, Seattle is not the Solar Capital of the Universe, no more than Tucson is known for excellent coffee!
@ May 6, 2011 8:15 PM in copper panel radiatorif it is coupled to an otherwise cast iron radiator set, it will be cold moments after the thermostat shuts off the system. The physics gods will not be pleased.
Stay with cast iron and if they want warm towels, there are electric and hydronic towel warmers. I would put one of those in, in addition to cast iron room heat.
@ May 6, 2011 8:12 PM in New Boiler - Steel or copper pipes?nobody bothered to get him a torch for Christmas, eh?
@ May 6, 2011 5:24 PM in Heat Loss CalculationIt is one of those quirks of geometry. Solar gains to a surface and glass in particular are higher the closer to perpendicular the angle is. An oblique angle will reflect more, an angle approaching perpendicular will cause more to be absorbed through the glass.
In the mid-day hours in June (the 21st to be extreme), the sun is at its highest in the northern hemisphere. A little bit of overhang will block much of it on the south side of a building.
Come November, this angle is lower in the sky so the gains are higher. (We actually have to air condition, cool, some spaces especially in commercial buildings because of this.) Now, in December, the angle is lower still, but the outdoor temperatures tend to be colder then, to cancel out some of the gains.
Consider that at the 40th parallel, raw solar on glass can be over 200 BTUs per Hour per SF of glass and with absorption and reflection, shading taken into account, is still often over 100 BTUH/SF. A room with a lot of glass can meet or exceed its heating requirement.
@ May 6, 2011 5:06 PM in Heat Loss CalculationI tend to work the numbers on an annual basis to even-out any anomalies over the year. Just a different way to think about it. The only down-side to focusing on monthly totals is that, for example, degree-days aside, November often shows higher solar gains versus temperature. (Moderate outside temperatures and more direct sunlight to vertical glass at a lower solar angle, as one example).
Not a huge deal though. By your reckoning, you have a solid grasp of the numbers, the values and variables.
If you have ever learned navigation with a sextant (way before GPS! And years ago for me...), you take three fixes, plot them and accept your location as the center of that triangle. I think you can do that, grasshoppa.
But DO try it over an entire year or two, just to see the effect of the total year. I would be interested in what you derive.
@ May 6, 2011 2:18 PM in Heat Loss CalculationThe baseline for HDD in residences is typically 65F. This is actually a bit outdated as it reflects construction that is a generation old. It is based on the notion that you will be "spotted" between three and five degrees due to internal gains, before you will need to add heat.
In modern construction, SIP or foam panel construction, this "balance point" can be in the 50's. I have seen it in the mid-high 30's sometimes. But 65F is the basis. I get from the same site 5132 HDD for 2009 and 4810 for 2010, an average of 4971.
Keep in mind that this is an annual event, so use the full year.
I will have to pick this up on the other side of a meeting I am now leaving to. Will check back later.
@ May 6, 2011 1:14 PM in New Boiler - Steel or copper pipes?Not to step in, but yes, iron pipe is capable within reason of supporting more weight including ancillary items such as circulators, air separators and expansion tanks. Copper can too but not as much. If you DO use copper, I recommend a hanger on each side of an item such as a circulator or expansion tank, allowing very little cantilever.
@ May 6, 2011 1:04 PM in copper equalizerWhile the above waterline piping and below waterline piping can and do share the same temperature ranges within a few degrees, the rate of change below the water side is relatively slow.
Above the waterline, going from room temperature to 215F in a few minutes -and back again to room temperature in minutes as well- is tough on copper. Below the waterline, you will never get much above 210F and it will take 15-20 minutes to go from room temperature to whatever peak you do get below the waterline. It likely will be cooler than 200F and once warm may get to room temperature some hours later.