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Why is it so important to drive the heat up?
Last Post 03 Feb 2008 08:05 AM by BenMiller. 9 Replies. |
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BenMiller
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Posts:95
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| 28 Jan 2008 11:36 PM |
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This is obviously a no brainer for many of you, but I must be thick headed, so I'll go ahead and ask...
Why is it so important to "drive" the heat up? If the fiberglass batts aren't there to push the heat up, won't the heat radiate down instead? In my case that doesn't seem so bad since the bedrooms are all on the second floor where we'll want to keep it a bit cooler for sleeping anyway, and the main living areas are on the main floor. I've also got Pex in the basement slab below all that main floor living space, so I'm hesitant to stuff the main floor system full of batt insulation fearing the heat from the slab won't reach the main floor (to help out the staple up). (my floor plan is 30'x32', full basement with an open stairway)
And while I'm at it, I can't afford the aluminum dispersion plates. So my tubes are stapled up to the subfloor with a layer of double bubble reflective foil installed 1-2" below. I can't afford the aluminum plates because I spent the money for SIP walls, ICF foundation, and closed cell foam everywhere else. My heat loss calculation came back at 24,000, and I installed a 34,000 btu Electric boiler (I can get electric at 5 cents/kw and the boiler cost $700 after the $350 rebate). From watching my meter run when only the boiler and pumps are running it looks like it can never cost me more than $50/month. (but I don't know if that $50 will keep us warm when it's -20 like it was here last week)
I've got 1/2" Pex on 8" centers on the second and main floor, and 3/4" pex on 16" centers in the basement slab. (NRT.rob you were correct on the heat striping at start up, but that seemed to even out after 3 days, now it's a consistent 64 to 66 degrees.)
As an aside, I don't have sheetrock up yet, but they say they will be here Thursday January 31, so the fiberglass batt question is pressing heavy on my mind. I think I got suckered on the double bubble foil, but it's up. Is there any other alternatives to fiberglass? I thought about XPS sheets...
It was in the 40's here today, so I can't really tell how the system does at heating my house. It made a big difference when they foamed the roof deck of course, but a better test comes later this week when temps won't go above 20.
P.S.
Any ideas as to why my water temp can't seem to get above 110 F? It's bringing my main floor and upstairs to about 60 to 65 F, and the basement to 75, but again temps where in the 40's today. It'd be great if I could keep warm and only run 110 degree water, but I'm having some doubts.
I've added a pic of my system as it looked when we first fired it up 2 weeks ago, it looks better now but you get the basic idea. Sorry about the lighting, camera phones can only do so much.
Feel free to rip apart everything I've got going, this is cyberspace and you won't hurt my feelings, you'll probably actually help me in the long run. (I'm a young builder looking to learn on my own dollar and my house is my $200k experiment)
Don't hold back, (even mikeinnyc)
Ben
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mikeinnyc
New Member
Posts:47
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| 29 Jan 2008 06:20 PM |
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no sheetrock..I've been there. Unless you spray foam everywhere, rock will help dramatically. Using 5/8X" worked well for me. no ceiling rock either w/ staple up? That hurts ouch! my bet is on the missing rock!!! Open your windows a crack its like the same thing. I love the spray foam. Nice job. Since your house is air tight you can get away w/o plates.
Also most important when you remodel is that Heat loss may be temporarily greater than your boiler BTU first hr rating?? Cut the heat loss then see. Electric at 5 cents makes me drool.....I pay 5 times that! However, electric is slow to recover btu's unlike oil or even gas which is faster btus back in your system.
100' of pex is like 1 gallon of water to heat up. How many feet of pex in total are you heating (gallons of water)? thus how many gallons of water are you raising to 110F? Can your little red $700 electric boiler handle the rating? I think you should put up the rock then try. Delta T gone wild with you.
Worst case is that you undersized your boiler or incorrectly calculated your heat loss.
50 bucks a month to heat that size home is a dream to me. therfore, based on what you stated:
1) Heat loss is greater than your finished design (house is not complete yet).
2) Boiler is undersized - remember electric is sllooooooooooww to recover. but 5 cents man oh man.
put up the rock see what happens. hey for 200k I'll take ten homes like that one. That's amazing. Do you use slaves? just kidding.
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| MIKE IN NYC |
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BenMiller
New Member
Posts:95
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| 29 Jan 2008 11:57 PM |
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Mikeinnyc-
I just came from my place, the temp outside is 0 degrees F, the wind is gusting to 40mph. (no lie, check the weather for 52240, southeast Iowa) Still no rock installed, but my attic is 55, main floor is 63, upstairs is 63, and basement is too hot for me at 78, (the slabs actually reading 84 degrees). Water temp is 110, and I'm not running the pump for the main floor loops, so they're just sitting there.
I'm raising about 30 gallons of water to 110F when all my zones are running. Where on my boiler would it answer your question?
I started stapling up more of the double bubble foil tonight, and then gave up because I was sweating. I wonder if maybe the spray foam on the rim joist, and sheetrock on the bottom of the floor joists will come work. Anyone want to buy 1000 sq ft of double bubble foil?
Ben
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NRT.Rob
Veteran Member
Posts:1741
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| 30 Jan 2008 10:23 AM |
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Allowing radiant heat to radiate down results in uncontrolled downward heat gain and, likely, underperforming upper levels.
Think about it. Thermostat on 2nd floor has a hard time satisfy and just runs and runs (hypothetical situation) dumping heat down. the 1st floor get hot.. shuts off... and just keeps getting hotter anyway, because it can't turn off the 2nd floor.
Foil in joists works (at first, at least). I just don't trust it long term and that is why I spec fiberglass. That is a controversial recommendation, not gospel, but it's mine ;). If you have it, put it in.
However heat loads are always "all bets are off" in unfinished homes, period. I would wonder why your slab is overheating so much. I would expect the slab floor to be off because of the heat dump from above. Perhaps a wiring problem?
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| Rockport Mechanical<br>RockportMechanical.com |
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mikeinnyc
New Member
Posts:47
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| 30 Jan 2008 11:29 AM |
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I agree with Rob. All bets are off until the house is finished. I didn't realize you used 3/4 pex in the basement 1/2 everywhere else. I believe balancing is an Issue now.
Since you have a small heat source balancing will be more important for you. Big BTU boilers (higher operating costs) are forgiving with plenty of overkill btus per branch if needed. You don't have that option yet. Can you or do you have a ball valve?? on your basement zone. Close it 1/2 way and measure your setpoint upstairs......then shut it off completely (pump too) and measure the setpoint again upstairs. Hopefully, you will over shoot your setpoint upstairs. If you can't get upstairs hot (basement totally off) or to where your desired setpoint is you need to increase your BTU source or pump speeds. From looking at your bright saturated cell phone picture I do not see any valves.
Ball Valves should force the flow to the other zones hopefully. Also, the hottest flow is on the first T and the coldest flow on the last T but I see your pump is facing down vs the other 2 facing up. If this is a closed system I believe its no problem. Are their spacing requirements for an electric heater specifically the distance between T's?
What do you think Rob? |
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| MIKE IN NYC |
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NRT.Rob
Veteran Member
Posts:1741
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| 30 Jan 2008 12:51 PM |
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that doesn't address overshoot in the basement.. that can't be caused by flow, if the thermostat is working.
no way there should be an 84 degree floor in a basement unless it's been running, and it shouldn't be running if it's 78 degrees down there. Maybe I'm missing something, but that would seem to be an issue.
balancing will be an issue though. hope there are flow meters on those loops... or, that might answer the zone pump vs zone valve question on this project.. |
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| Rockport Mechanical<br>RockportMechanical.com |
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mikeinnyc
New Member
Posts:47
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| 01 Feb 2008 12:56 PM |
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Ben, when your Zones require different supply temps because of of different materials IE: Cement Slab (low temp) zone one VS. Wood Staple up w/o Plates (higher temp) zones 2,3 you must :
Use a zone valve (or valve actuator) on each circuit to allow adaptive control.
See Figures 16 and 17 for typical uses of zone valves and valve actuators.
These diagrams also show the use of multiple manifolds – either where needed
because of the zone size or because multiple temperatures (differing by more
than 10 °F) are required on the same or multiple zones. (Page 16 Weil McClain link)
Unfortunately, you need to isolate, completely stop, and or modulate the flow of BTU's to your basement zone, before you overheat the cement slab.
I am certain this is your issue. I'm willing to bet the your pump keeps pumping due to its zoned thermostat. I assume you have a slab sensor embedded in the slab? Use better thermostats, specifically 501s with both (air and slab temperatures) otherwise .... you might always overshoot the temp in the basement with a cheaper air temp thermostat. I am assuming you have no air cavitating in your pumps restricting flow upstairs, and no gravity flow of hot water to basement zone with pump off. Does your Grundfos have IFC flow control or check valve to prevent this?IF not TACO makes a 00R-IFC Radiant Heating Circulator which should solve backflow problems, but not modulation problems. If you want to balance your system by BTUs link below.
http://www.taco-hvac.com/en/products/00R-IFC%20Radiant%20Heating%20Circulator/products.html?current_category=54
http://uponorhsdna.com/index.php?id=122&pid=19
http://www.onicon.com/System30.shtml
Let me know if this helps out,
Mike
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| MIKE IN NYC |
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BenMiller
New Member
Posts:95
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| 01 Feb 2008 10:48 PM |
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Mike,
I'll need to get with my electrician to see how the thermostats will be wired when we finish, but right now I have a cheap knock around thermostat in the basement and all zones are wired to it. At the very end, he will wire each thermostat individually to each pump, and I suspect I will have to add some valve acuators to my system to keep the slab temp loops lower than my staple up temps. After checking with my boiler installer I discovered he's only done radiant in slabs, never staple up. We'll see where this ends up.
My Grundfos pumps do have the check valve installed, but since the basement loop pump is installed upside down...
I think NRT.Rob is right, that all bets are off until the construction is complete.
I don't have a slab sensor embedded in my slab, is it possible to surface mount something?
Ben
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mikeinnyc
New Member
Posts:47
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| 02 Feb 2008 09:32 PM |
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Ben,
You need to add some cash to finish your radiant system. Cheap way out is to just add a wirsbo 501s with slab sensor. You can't get away without the slab sensor. Don't cut your floor now!! just use trough and embed it in 1/4" Thinset for Ceramic tiles or special thinset for stone...or whatever. You will have to add thinset on top of cement anyway so thats fine. Just embed it in asap!
This should be the end of you overheating in the basement and freezing on the other floors. Think about it for a second. Once your "slab" is up to it MAX ALLOWED SLAB temp 80 maybe (depends on your preference) it will turn off! Your air temp will not be at set point and maybe still cold. Since the slab sensor reports the temp to your thermostat your thermostat immediately turns off your PUMP for that zone stopping the flow. Then the other pumps can fight over who gets the rest of the hot water Limited BTUs. That is the balancing question you need answered Maybe? There's more BTUs available now since the slab zone was satisfied. Eventually, minutes or hours after your slab reached it's temp your basement will reach its air temp without overshooting the airport. Your other zones will get the needed btus not hogged up by the basement.
Its the Mars Rover signal from NASA on Earth it takes up to 30 Min's delayed reaction... so stop 30 Min's ahead.
I can help you with your wiring if your guy can't.....since your Pump relays look homegrown. Tell your boy to PUMP away and UP not down. Air bubbles in your slab pump will rise up wards causing cavitation and a wasted pump in few weeks. I'm sure its temporary right? I see that you already have a PUMP controller so you could definitely use this as long as you understand plastic spaghetti wiring associated with that Controller. Since your pumps already have flow control IFC this is just as good as a check valve so you won't need any ball valves since your pump won't allow flow when its off...and installed correctly.
Your low voltage thermostats should not be wired directly to your high voltage 120vac 60hz pumps. I know what you mean.
Now if you want more specific BASIC control???
You have 3 zones right? Basement/1st/2nd/ maybe attic in future? that would be 4 or more depending.
at a minimum:
*You need a 3 zone Switching PUMP relay or Greater. If a few bucks more buy the 6 zones. YOU have this yes?
TACO.com makes a High Quality/ Totally supported/ USA made. Note; The priority is for DHW Indirect storage TANK for your hot showers,bath, dishwasher. Do you have a separate heating system for the DHW? If so you won't need a Priority Zone for SR or ZVC.
pick one of these. PUMP controller only! If money difference is nil get the 506.
SR503-EXP 3 Zone Switching Relay with Priority and 3 PowerPorts
SR504-EXP 4 Zone Switching Relay with Priority and 3 PowerPorts
SR506-EXP 6 Zone Switching Relay with Priority and 3 PowerPorts
Zone Valve Controllers one for each pump. Again check the prices if a few bucks more buy the max 406. Then upgrading won't be painful. The ZONE Valve Controller is for ONE ZONE ONLY -EBV/BALL Valve Zone Controllers/or thermal actuators. you can't buy one ZVC and use it on all three or even two zones. At the min just buy one for the slab so that a ball valve(if your pump has IFC,expensive and your good) will close off the cement slab zone when the temperature SLAB sensor reaches it's desired temp and N/O opens your thermostat or off mode.
ZVC403 3 Zone Valve Control
ZVC404 4 Zone Valve Control with Priority
ZVC405 5 Zone Valve Control
ZVC406 6 Zone Valve Control with Priority
In short, you do not need these IF you are satisfied with your CONTROL OF your Radiant HEAT. Overheating and under heating you have no control.
Mike |
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| MIKE IN NYC |
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BenMiller
New Member
Posts:95
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| 03 Feb 2008 08:05 AM |
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Mike,
Thanks for all your help, I'll work through that message when I can finally get all 3 zones on their own thermostat. I've seen the Wirsbo 501's and plan on using them, so I'll thinset in the slab sensor then.
When Evan installed the pumps I asked about the upside down one, and we looked at the Grundfos literature and their pictures show the upsided down mount is ok, but I still have questions. I guess when it dies he can replace it with one of the Taco's.
Thanks again,
Ben
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