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Heat Loss vs. EDR??
JJ_4
Member Posts: 146
I understand the difference between steam and water for the same radiators.
However, if I switch to hot water I don't (can't the steam is one-pipe) plan on using the existing radiators. My re-phrased question now is:
If I put in new panel radiators, or baseboard, or radiant floor, and make sure I have the equivalent BTUH from the new radiators vs. the old, then could I get away with the BTUH from the EDR calcs rather than use the heat loss calcs?
Don't worry, before I would make such a drastic change I would have my contractor verify my EDR and heat loss calcs.
As far as the solar gain; it keeps the boiler off pretty much all day even down to the upper-30's. Typically, the mass has released its heat by about 9-10 PM and the boiler kicks in for the night. I'm in Colorado, so the sun is a reliable heat source for 75-80% of the time.
Thanks, JJ
However, if I switch to hot water I don't (can't the steam is one-pipe) plan on using the existing radiators. My re-phrased question now is:
If I put in new panel radiators, or baseboard, or radiant floor, and make sure I have the equivalent BTUH from the new radiators vs. the old, then could I get away with the BTUH from the EDR calcs rather than use the heat loss calcs?
Don't worry, before I would make such a drastic change I would have my contractor verify my EDR and heat loss calcs.
As far as the solar gain; it keeps the boiler off pretty much all day even down to the upper-30's. Typically, the mass has released its heat by about 9-10 PM and the boiler kicks in for the night. I'm in Colorado, so the sun is a reliable heat source for 75-80% of the time.
Thanks, JJ
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Comments
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Heat Loss vs. EDR??
My basic question is: for sizing a boiler and radiation why aren't BTUH's output from water the same as what I would need for BTUH's from steam for the same house??
If you can point me to one of Dan's articles I haven't read, then you can stop reading now; otherwise here are more details:
As a homeowner with a steam system I have calculated my current EDR and understand from this forum that this is the way to eventually arrive at a boiler size for a new steam boiler. The EDR is 267. If I multiply this by 240, then the BTUH is 64,080.
I also did a heat loss calculation using the SlantFin program; thinking I may want to swap out to hot water heat. The total is 91,864.
Looking to try to reconcile these numbers I broke the numbers down into the 2 major areas of the house (it is a 80 year old grocery store that has a very open loft style plan as a home).
The results are: For the 462 sf (id) north area heatloss and EDR match closely 34,080 (EDR) and 34,325 (Ht loss). For the 770 sf (id)south area (which has significant solar gain from 240 sf of glass and glass block)I get 30,000 (EDR) and 57,539 (Ht loss).
The building is situated lenthwise S to N, 24' wide, 58 ft long, 1ft thick brick. I also get a lot of passive solar gain from the long west wall and an additional 60 sf of glass block that wraps around from the south to the west side. The north area was the original living quarters for the store owners, the south area was the store. I've added R-30 insulation in the attic; which was accounted for in the heat loss calcs.
The home is very comfortable with the current radiation; if not a bit too warm in the north area.
I think you can see where I am going...If I convert to hot water and use the EDR BTU's as a design baseline, then I could use a 90% efficiency boiler of a much smaller size (especially from the current oversized steam boiler), and be able to take advantage of lower water temps through outside air reset and solar gain through zoning, etc.
I plan to discuss this with my local contractor, but any input would be appreciated. Am I comparing apples to oranges?
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EDR- Hot Water versus Steam
It all has to do with temperature difference, JJ.
Steam in a radiator at 2 psig is 215 degrees. In a 70 degree room each SF of EDR will emit 240 BTU's per hour (BTUH) when maintained at that temperature.
In hot water at 170 degrees average water temperature (presumably 180 in/160 out but it could be 190 in and 150 out, same thing), the value drops to 150 BTUH in a 70 degree room.
With minor deviation it continues as a slope until the radiator and room are at the same temperature, whereupon the output to the room is zero.
This is why outdoor reset works so well and temperature to output is the best principle on which to control a system.0 -
Point #2
It would seem that your radiator take-offs are low or your heat loss calculations are very high. Because are you properly heating the space today, I am guessing the latter and the solar gain is helping too. But remember solar gain does not help you at night; only storage of solar heat in the structure mass does that, and only for the time it takes to come to equilibrium.
In general terms I have found that a steam heated house with radiators designed for uninsulated conditions will perform well with hot water if the house is insulated and sealed well. In short, you lose a third of the capacity output from the radiators but you also lose a third or more of your heat loss. A true calculation is still needed, this is an order of magnitude statement.
If the radiators perform as you need them to, condensing boilers will be outstanding, especially with TRV's on the radiators.0 -
EDR versus Heat Loss
Using radiator measurement and calling it heat loss is folly, JJ. While it may have been sized "exactly" to the heat loss so many years ago, does not take into account any envelope improvements. Nor does it confirm anything but one thing: How much heat can the radiation emit to the space at a given steam/water temperature and room temperature?
That is it really: EDR is a radiator measurement.
Your heat loss is a function of all of your various surfaces plus infiltration.
How your radiation (measured in BTU's per hour or EDR) stacks up against your heat loss tells you if you have enough and also tells you by back-calculation, what water temperature (how low) you will have to run to meet heat loss on a design day. From that point the heating curve can be plotted.
BTW: I would not write off re-using the steam radiators yet. If they have bungs on the corners they can be removed (WD-40/Liquid Wrench and a wrench with extra leverage gently applied.) Also the vent tapping can be plugged and an air tapping drilled and tapped. There may be a dimple for that purpose high up on the radiator. It is commonly done.
But if you do opt for panels or fin-tube or radiant floor, I would watch a few things:
1. Do not mix the types on one zone. Cast iron with cast iron, aluminum/copper with same. Panels can be used with either provided you use constant circulation and TRV's.
Personally I favor [EDIT: Second to Cast Iron if you have ruled that out], radiant panels with TRV's alone or in addition to radiant floors. RFH is the best
2. Select new radiation all for the same average water temperature. Generally I use 120-125 F AWT (140 Entering and 100-110 leaving) for condensing design work and on a design day. This will reward you with condensing for most if not all of a given season. If you re-use any old radiation, de-rate it accordingly to be consistent.
By having a consistent water temperature you may be able to get away with producing one temperature from the boiler/plant. Otherwise you will have to provide mixing valves and devices for various "flavors" (temperatures) as may be needed.
Hope this helps.
Brad0 -
Steady up there Brad. Love all your posts and read them all but i have some recollections of you saying that CI rads were king. Why the switch to european emitters.
ps. I was planning to replace my fin tube BB to CI rads to compliment my Munchkin and improve condensating.
your present thoughts thanks Brendan0 -
Good time for clarification
Thanks for the kind words, Brendan.
You are right to call me on this and it is more a matter of clarification; choices within choices. I will edit it to make it more clear.
I stand by my original concept that cast iron is king. It emits a deep penetrating heat that holds over time, no doubt. It is a classic form of heat and when one has it already in abundance (an older house) I would encourage a HO to keep it -much as I did in my posting above.
Issue becomes trying to supplement it or in the case of this thread, what if keeping it were not desired for any reason? From that perspective (cast iron out of the running), then I would favor radiant panels among above-floor emitters.
Some places do not have a surplus of CI rads (midwest where there is not a lot of hydronic heat) and they do not ship well compared to panels. Sometimes it is impossible to supplement cast iron with ones of the same style. Some folks cannot tolerate the space they take up.
Personally, in my house, I have both and with TRV's. Runtal in about 80% of rooms. Cast iron in my dining room and mud room plus basement. (A mish-mash of styles, it is a basement after all.)
Thanks for your comments!
Brad0 -
while on this topic
Brad thanks for quick response as always "you are a wonder"
If the EDR of a radiator is known and the average water temp is estimated is it fair to say that the,
BTU output= EDRxAverage water temp
or are there any other factors involved
Thanks Brendan
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Aww shucks...
Thanks, Brendan. Appreciate that.
Try this link:
http://www.colonialsupply.com/resources/radiator.htm
There is a handy chart with a generally acceptable curve. Almost linear, really.
The output is a ratio between average water temperature and the room ambient. The potential output naturally and rapidly diminishes as the two temperatures come close together. The chart on that link is for a 70 degree room. A short synopsis is:
AWT / BTUH per EDR
100F / 10 BTUH
110F / 30 BTUH
120F / 50 BTUH
130F / 70 BTUH
140F / 90 BTUH
150F / 110 BTUH
160F / 130 BTUH
170F / 150 BTUH
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Great
chart! Thanks for sharing.0 -
shareing
Yes Brad thanks too for shareing as always
Brendan0 -
Just an observation
If "Using radiator measurement and calling it heat loss is folly..", then why is this the way that is recommended for sizing a replacement steam boiler??
The way I have understood postings here and from Dan's writings: If the space is comfortable, then the EDR is probably OK. Of course, it is wise to verify with heat loss calcs.
After this, you can obtain savings with a new steam boiler of higher efficiency and by avoiding the oversizing problems caused by the legacy of the original coal fired unit and the unit that was probably oversized to replace it in the 60's or 70's.
By the way, I just got Siegenthalers Hydronic Studio software. South area loss = 38,136, North area loss = 23,529. This does line up closer to the Dead Men's radiation.
Thanks for all of your help. I appreciate your time and knowledge.
JJ0 -
EDR versus Boiler Size
Fair question.
Steam boilers are rated at the amount of EDR they serve, based on the amount of steam they can produce based on an hourly rate. The volume of iron if you will, governs. If you connect a 500 EDR boiler to 600 EDR of radiation, the radiators will not heat all the way across or not evenly. The steaming capacity peters out before the radiators are warm. If the EDR is matched to heat loss, all is good, but the (steam) boiler then has to serve the connected radiation of whatever total capacity it is.
Water boilers are sized to heat loss. If you have too much radiation (AS-IF!) all that means is that you can run a lower water temperature to them. Hard to beat having THAT problem!
In a water system, the media (water) is always in contact with the radiator metal. Under continuous flow especially -but under intermittent flow as well-, heat transfer is at a constant rather than cyclical occurence albeit at a varying rate.
With steam a cold radiator is a cold radiator, with water there is some residual heat because the mass of water of a given volume is 1700 times that of steam. Gas versus liquid. And when steam is not present, the radiators are filled with -air at room temperature.
Off the cuff, that is how I would explain it. Hope it helps! And if not correct in any way, I appreciate alternate explanations.0 -
Brad,
I would also like to point out that there is a similar chart in Dan's EDR book, within the first few pages.
Now this is for J.J. The EDR is the only way to size a steam boiler for EXISTING radiation, when being replaced with STEAM. The variables with water temperature don't apply here, as steam will ALWAYS be at least 212°. Thats what water boils at, at sea level anyway. The replacement steam boiler HAS to fill the connected radiation for it to work to its best and fullest potential. Key word being potential.
Like you've stated, the connected radiation can make the same amount of heat/BTU's, with lower water temps according to the charts, because... The load has changed due to envelope improvements, thus you could make the needed heat with lower temps. and still be warm.
I too agree with Brad on emitters. My first choice would be high mass radiant (if the budget allows, there just isn't anything more comfortable) Next would be C.I. radiators followed by panel rads and finally baseboard. Mass has appeal to me. I've been in this trade for over 20 years now and wish I could count the times that a homeowner has told me that getting rid of their radiators was the biggest mistake they ever made.
Panel radiators come close but given the choice....I would still (and do) keep the radiators. TRV's are going to be my next step. The Euro heat model is something to behold. Most of the places are built to heat with 130° water, to make that condensing boiler worth the price of admission.
Best of luck in your endevour, and please use the find a pro link when choosing the contractor for your new heating system. Like you, if they don't know....they know who to ask! Chris
Brad must type way faster than me!0 -
But isn't he asking...
why he measures only 64,000 BTU/hr of existing CI steam radiators (sounds small) but calculates the structure heat loss to be 92,000 BTU/hr, in spite of the observation that the structure stays warm enough w/ the existing radiation?
Sounds like he's undermeasured the total EDR of the existing radiation (possible), overestimated the heat loss of the sttructure ((likely) or some of both.0 -
Which was my second point...
See posting "Point #2".0 -
JJ, recheck your heat-loss
I think you're missing something. Typically old radiator systems were oversized. Maybe someone removed radiators from the system, that would also explain the boiler size. You wouldn't want to do all that work only to not be able to heat the house, right?
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