new system design sanity check

Boon

Hi. I'm a homeowner who is planning to convert forced air to hydronic cast iron baseboard (did I fail the sanity check already?). I've been lurking & reading up for a while. Every time I think I know what I'm doing, I read another thread that introduces a "wrench" into my plans. Would really appreciate some feedback.

The house is small, two story, 22 x 26 foot print + a 10x11 sunroom. The manual J (wrightsoft) says 30k BTU for the entire house. I was planning on a home run system, 4 zones: basement - 7000btu; sunroom - 4100btu on 1st floor; remainder of 1st floor - 8500btu; second floor - 9600btu. The folks who did the manual J suggested a Weil-McLain Ultra 80. I'll add indirect domestic hot water. [edit: added floorpan to the post]

The main plan is/was to run 1/2" pex-a-pex to each baseboard (13 or 15 of them); the shortest piping run is about 20' and the longest is 80' - average length is 45'; I'm planning on a few pex manifolds with actuators; one pump for DHW, one for circulating to baseboards, one for boiler. I think I need a buffer tank to hold some thermal mass or I risk short cycling.

First, things that trouble me:

1. Zones. Truthfully, I really want each bedroom to have its own thermostat. I don't want to use thermostatic rad valves. BUT I've read that making each room its own zone with such little BTUs (
2. I've calculated flow rates that are absurdly low to each of the baseboards. This is the part that troubles me most. I've seen other posts regarding low flow rates in a similarly designed system but I didn't see an obvious answer that made sense to me. I suspect actuators solve this, no? Or perhaps a ∆T pump or ∆P pump solves this. Or both a ∆? pump and actuators. For either a 20 or 30 degree drop in temperature I calculated either 3GPM or 2GPM, respectively, but each zone or baseboard is coming in much lower. Like this post but honestly I didn't see where the question was answered.
   
3. I'm having difficulty sizing the baseboards. It seems obvious that if a room has heat loss of 510 BTU that 1' of baseboard with supply water at 180F and 4GPM would do the trick (baseboard specs). But, (1) I thought the boiler will deliver whatever temperature water it needs, based on outdoor temp and how long it takes to satisfy thermostat(s), and (2) want my return water < 130 for the condensing... these two items have me a bit confused about sizing. What am I missing here?
   
4. Someone described a similar system to the one I am trying to plan and a professional commented, "Why zone that?" ... Because I want temperature control, right?
   

Next, a list of things that trouble you? ...

If someone can make sense of this post I'd appreciate some pointers in the right direction. I feel like I have a decent level of awareness of all the variables and equipment but I'm missing some fundamental understanding of how each variable interacts with the others, or something.

Zman

A couple quick thoughts:

How did they go from 30k to 80k? That will short cycle.

If you are piping primary/secondary, I would not get very worked up about flow rates to the emitters. Calc the minimum and don't get too worked up about ending up a little higher.

If you want to get high efficiency out of a high efficiency boiler, you must size the emitters based on the lower water temps. You could do miles of baseboards or panel radiators like Runtal. Just pick you water temp and look up the output for the model you are looking at.

If you size your boiler correctly and add a small buffer tank, you can probably micro zone the system as much as you like.

Consider that a 30 gallon buffer tank will store about 5,000 BTU/Hr at a 20 degree delta. A boiler that could turn down to 10,000 BTU/HR would run for 30 minutes heating the tank with no zones calling.

hot_rod

If you have a room with a 510 BTU/hr heat load that is considered a micro load, no gas fired boiler I know will turn down that low, and the number is on design day.

As Zman metioned a buffer tank or a boiler that is a tank style, like the HTP may be the best option.

With home runs you could have several rooms on one t-stat, just balance the various heat emitters at the manifold. low temperature operation increases the baseboard or panel rad size, you will need more than 1 foot if you want to run 120° SWT, which would be a nice target.

I'd have you reconsider panel rads and TRV, they really are an excellent way to cover low temperature control.

Brewbeer

I just went through this very exercise: ditching forced air for hot water baseboard. Check out the thread on my project: http://forum.heatinghelp.com/discussion/154385/fha-to-hwb-conversion-project/p1 Even though it was at least double the cost of replacing the furnace, it improved the comfort of the house by a factor of ten. Totally worth it, and I would do it all over again.

0) First things first: With a heatloss of 30k BTU, the Ultra 80 is at least twice as large as it needs to be to match the heatloss. A smaller boiler is recommended.

1) Zones: The advice given to me was small zones require a buffer, so I installed one (30 gallon). This may be less of an issue with cast iron vs. fin tube since the cast BB holds more water and therefore can act like a buffer. The No. 9 Snug baseboard holds about one gallon of water per 3 feet, not sure what you are using or how much water it holds. If you have 90 feet of Snug baseboard in your project, that's 30 gallons right there. Need someone with more knowledge to weigh in on this one.

2) Flow: Design for 1 GPM, it is more than likely plenty of flow. The difference in output of the baseboard between 1 and 4 GPM is small. The flow rate through my system is down in the 1 GPM per zone range when all 3 zones are running. I ended up with a ∆T pump with zone valves; the pump never runs above its lowest setting other than the first couple minutes of operation.

3) Sizing Emitters: Size the baseboard for less than 170 AWT at design if you want to be condensing most of the time. I sized mine for 130 supply to stay in the condensing range all year, but the ∆T for cast BB will be higher than fin tube. Consider sizing for 140 AWT, but note doing so will add about 50% to the length of each baseboard. You are correct, the temp delivered to the baseboard will be modulated by the boiler using outdoor reset. This gets set up once the boiler is installed.

4) It's your house, get the system you want. It will cost more, be more complicated, and may require you to install a buffer tank, but hey, it's only money, and you are paying for the comfort. After all, that's why you are ditching the forced air.

Keep the questions coming, you will definitely think of more.

Brewbeer

One more thing: when sizing the emitters, don't forget to de-rate the output of baseboard by 15% to take into account that the baseboard manufacturers association allows them to overstate their output by 15%.

Boon

Thanks for the replies, folks.

@Zman said >>> go from 30k to 80k

I guess I'll have to ask them. I assumed they spec'd that boiler since the boiler mods down to 16k and because I was adding DHW. They asked if I had a boiler/brand preference and I said, "I want high efficiency and how about Weil McLain." I'd like to think if WM didn't have a suitable boiler they would've said so and spec'd a different one.

@Zman said >>> 30 gallon buffer... 5000BTU/HR at 20 degree delta... A boiler that could turn down to 10,000 BTU/HR would run for 30 minutes heating the tank with no zones calling.

ok, this shows how green I am. I can't tell if this is good or bad, but from hot rod's comment I think it's good.

@hot rod said >>> If you have a room with a 510 BTU/hr heat load ... reconsider panel rads and TRV

Sorry - I only used 1' and 510 as an example, although my lowest room isn't far off. Panel rads don't fit the character of the house & TRVs were also bumped for aesthetic reasons.

@Brewbeer I'm envious! That thread is both intimidating and encouraging. I never noticed the 15% nonsense factor! Good call.

@Brewbeer said >>> Design for 1GPM... size for 140AWT ...

I'll give this a try. I think I'm getting lost because everything is variable: The baseboard length can vary; the GPM can vary; the SWT can vary; the boiler can modulate; ... I have this expectation that I should be designing from some foundation and I don't know what the foundation is. I might need to go back to square one and read some more.

Thanks for all the comments, all. I'll go back to the drawing board...

Zman

You do not need to upsize the boiler for DHW. You will be setting it up as a priority load.
I would go with smallest mod con boiler you can find and pipe it with a buffer tank.
Check out this http://www.caleffi.com/usa/en-us/technical-magazine.
#17 has the some great stuff on systems like yours.

Rich_49

@Boon said
" I guess I'll have to ask them. I assumed they spec'd that boiler since the boiler mods down to 16k and because I was adding DHW. They asked if I had a boiler/brand preference and I said, "I want high efficiency and how about Weil McLain." I'd like to think if WM didn't have a suitable boiler they would've said so and spec'd a different one. "

There is a distinct possibility that they do not know . They asked you what kind of boiler you were thinking of ? Most contractors may ask this question but then recommend something other , certainly something more proper for what it is you or another want to do . Considering what you want to do makes sense , which your wants do .

So now you are faced with what so many others deal with , does my contractor have a clue ? What should I do ? This is more complex than I thought , forget it ! Boiler , indirect , buffer tank , primary secondary piping , 3 circs , hydraulic separation , this is quickly turning into a 12 chicken a day alligator !!!!!!

In a house like yours there is no way around leveraging mass or storage capacity , just aint gonna happen . All those components and all that there complicated work with all those components lessen your chance of a good install ( unless one of us is near you) , but even if one of us is near you there is still quite a material list of more than inexpensive components .

The first 2 products will perform flawlessly in any system with proper programming by someone who knows what the numbers mean . Forget the high side fire rate , the low end is what bites everyone , that's why there are buffer tanks .

If after you look at the links below you still want a boiler , buffer and indirect and all the chances you will take getting it done right find a 55,000 BTUh boiler from HTP , Lochinvar and the right indirect and call it a day . Those will only likely require a 20 gallon buffer tank .


http://www.htproducts.com/versahydro.html

http://www.htproducts.com/versaflame.html

http://www.htproducts.com/pioneer.html

You can make your own Versa Flame by adding 1 , 40 plate heat exchanger and one circ between the boiler and the flat plate using the Pioneer .

http://www.htproducts.com/phoenixldwaterheater.html

Although not shown being used as a hydronic heating source I assure you the following link will explain WHY HTP cannot at present show it that way . 2 circs , 1 flat plate heat exchanger and a Taco I Series reset mixing valve and your done

http://www.floortrendsmag.com/articles/96738-warmboard-introduces-new-radiant-heating-system

Yes Virginia , that is a Phoenix Light Duty !

Brewbeer

@Boon there are variables but the heat loss at design day is fixed. Based on a fixed heat loss per room, baseboard length will vary with water supply temps. Putting everything into a spreadsheet allows you to vary things like supply temp and easily recalculate baseboard lengths. The key to getting as much efficiency as possible out of a mod con boiler is low water temps, which requires longer runs of baseboard, which will cost more. If you want, PM me your email address and I'll send you the spreadsheet I used to run my calcs.

Alan (California Radiant) Forbes

Lots of good information!

And yes, panel radiators like Runtal look very modern, but they just seem fit in with any style of house. We've done a few Victorians in San Francisco where they look great.

Boon

Thanks for the push @hot rod and @Alan (California Radiant) Forbes We decided to go with the runtal baseboards and panels and will use TRVs.

And @Rich after designing a system around a boiler, buffer, and indirect now I'm started to plan a system using the HTP versa hydro and I don't understand why the literature says there is a "10 to 1 turndown ratio on the space heating module" What is there to turn down on a brazed plate and pump?

And if the space heating max is 100,000btu with a 10:1 turndown, that is oversized for my smallest zone. But it's a giant 55gallon buffer so ... I don't understand how any of this 10:1 turndown matters or how it impacts my design.

Rich_49

@Boon

Are you stating you are using Runtal Baseboard , panel rads , both with TRVs and are going to use a Versa Hydro ?

What there is to turn down when talking about the heating module are flow rates . Since you are leveraging mass in the tank it does not impact too much . Basically just running 2 circs during a call and burner only fires when necessary , maybe 10,000 BTUh would have been better stated as 1 gpm since the Versa's default programming recognizes a Delta of 20*. Your stored water temp in the tank should vary seasonally based on emitter temp requirements . Maybe you'll need 140* water at or near design , you'll be wanting to heat the tank to a higher temp , storing more BTUs there to be transferred to the space heating water . In non heating months maybe you only store at 140* (recommended for legionella protection) . The turndown of the combustion assembly is not 10:1 .

What are your loads at say 50* F ? What loads were you sizing a buffer for , design loads ?

Now that it appears you are using emitters that have TRVs this becomes less of an issue since you have the ability to have constant circulation with a tight ODR curve since you will surely base all your emitters on a particular temperature and bypasses here and there possibly at the emitters . The Versa will monitor how much heat is being transferred between the tank and the space heating fluid and vary it's speed accordingly.

Boon

@Rich thanks. I should've known it was a variable pump. And it was just yesterday after I posted that message that I realized with TRVs I'll need continuous circulation and need to learn how to plan & set that up properly. Siegenthaler's book is arriving this week and I desperately need it.

Rich >>> Are you stating you are using Runtal Baseboard , panel rads , both with TRVs and are going to use a Versa Hydro

Yes, that is the latest design I'm working on. I might've misspoke if "panel rad" is different than a Runtal panel; all our emitters will be Runtal, and I sized them based on AWT of 140.

Maybe I should size the rads for 150 AWT with the understanding that [far more often than not] outdoor temperature will be above design temp. Smaller emitters would save some cash & space. The original plan was to keep return 130 or less all the time but I can live with 130 or less most of the time.

Rich >>> What are your loads at say 50* F ?

I've been wanting to check this. I took the load numbers from the Manual J (that was given to me on paper) and typed them into my spreadsheet so I can't easily change the design temp to 50. It'll take me some time to do that and frankly I'm not sure if I'm willing to do that as all the calculating, changing, recalculating, changing, recalculating, ... is getting old!