Hydronic baseboard/ reset control question

Greg_34

Okay, that makes sense to me know. Initially with baseboards, i was anticipating the installation of a loop. Top tier/bottom tier under those circumstances would make the end of the loop very cold. The U-shape, supplying the avg. water temp makes sense with the install.

The argo's look good, now I just need to figure out what systems would be correct. Based on Slant/fins software, my unit has a combined heatloss around 65,000. How much overrating is allowable before the system gets inefficient?

-Greg

Greg_34

Updating a steam system

I'm currently evaluating what systems to install into my multi-family.

I'd like to convert my single zone one-pipe steam into two zone hydronic to separate the utilities. My chimney isn't in that great of shape so i'm leaning towards two direct vent boilers with either indirect heaters or coils.

for efficiency purposes I've also looked into reset controls, and here comes the question. After doing heat loss calcs and figuring what size baseboards are required for 180 degree water, will the baseboards need to be resized due to using reset controls?

Any referrals would be appreciated as well. I have a "new" 2001 burnham V8 which is currently running like a champ after purchasing Dan's books, venting the mains, replacing all rad vents on 16 rads, lowering pressures, etc. I'm looking for someone who might be interested in taking all my good working equipment as partial trade for installing two systems in my two-family.

Happy new year everyone,
Greg

Brad White_9

Generally speaking

yes, condensing hot water or any hot water with reset will work. (See note on the BNL study below.)

I personally favor sizing radiation for 140 degree entering water on a design day. 140 entering, 120 leaving so 130 average being the basis of selection. I use 20-degree to keep the flow rates high for turbulence. If I use 40 degree, the flow rates are too low and the average temperature drops to 120.. performance suffers and more element length is needed. But the point is, I select the radiation to perform at as low a temperature as can be afforded to increase efficiency for longer periods of the season.

In commercial/institutional work, this is practical and efficient because such installations can accomodate mulitple tiers, 4-inch square fins and other refinements.

THAT SAID, residential baseboard generally is limited to 2-tiers high, most of it is one tier and there just is not often enough wall to get the length you need if sized for lower water temperatures. If you get 550 or 600 BTU's per hour per foot at 180, you may get only 200 or less at lower temperatures consistent with condensing boiler design. (Actual manufacturer data is not at my fingertips, that is off the top of my head for order of magnitude.)

The best news I had recently on this topic was a posting citing a Brookhaven National Laboratory study (BNL-73314-2004-IR) which explored and confirmed that conventionally sized baseboard radiation indeed performed well with condensing boilers using outdoor reset (!).

Search for that link and download a copy. Good reading if you are into this sort of thing.

The study found that the hours of occurence where required boiler return water temperatures would promote condensing efficiency were predominant enough to make this a viable and financially sound decision.

On the engineering side, those of us that specify condensing boilers as retrofits for conventionally sized (180F) distribution have relied on "shoulder-season" savings. This study confirms that the savings window is wider than commonly believed in most temperate climates (outdoor design of 8 degrees on Long Island was the test house).

Hope this helps.

Brad

Greg_34

Thanks Brad, I appreciate the input. I'm new to all of this, but logic was telling me that lowering the temps of the circulated water would probably result in underheating with conventional baseboards.

I'm a little unclear whether or not you are implying that the BNL document found condensing boilers and reset controls CAN work with these types of baseboards, or whether i would need to increase their length. (which won't work due to space issues like you mentioned) I don't know what a 2-tier is, but are different baseboards available that would suit my needs for this type of install?

My desire is to go with the most efficient system, but do you think I'm trying to "over do-it"? Or am I headed in the right direction. Side note: I'm interested in gas as opposed to oil which I have now. Only because this will be a rental property and a gas bill is easier to organize with tenants.

Cheers,

Brad White_9

Hi Greg

What the study said essentially was that a system that was designed for the higher (normal conventional) temperatures, would still work fine with reset.

Not as well as other types such as radiant panels or cast iron, but well enough that baseboard (the most common type in budget installations) would still be worth applying reset controls to it. My suggestion is to increase length where you can just to get the system to operate with lower temperatures in general.

If you have 12 feet of wall and eight feet of baseboard heats the room with 180 F water, why not put in ten feet? And whatever that percentage is for any room, use the same for all so that the room heat is even with a given temperature. In other words, don't double the radiation in a room because you can, and not do that in other rooms.

Baseboard and Reset: Generally the output is linear but there is a drop-off at the lower temperatures. Stated otherwise, your low-end temperature will be higher than with other means of heat. You could get down to 100 degrees or less with radiant floors but maybe bottom out at 120 or 130 with baseboard. When you buy the controls, you will see what is known as "heating curve adjustment". This can be tuned for your particular needs. Too cool when it is 40 outside? Adjust the curve. Best deal in town.

Two-Tier means two elements stacked one on top of the other. This generally yields only 30% to maybe 50% more heat over a single tier. (Height is the issue in residential construction. Commercial BB is 24 inches or more high.) The reason for the diminishing return on heat output is that the heat output is relative to incoming air temperature. The first tier or single tier sees 65F off the floor and warms it to say, 110F. Now add a second tier and it is seeing 110 F so less heat transfer.
Reminds me, I forgot to add: Use counterflow piping: Pipe the top tier with the supply and the bottom tier has the return, with a u-bend at the other end. Leaving air sees hottest water. A good thing.

In terms of efficiency, generally whoever pays the heating bill pays the piper. If you the landlord pay the heat (built in to the rent) then it is your dime. If the tenants pay then it goes to marketing: Get and keep better tenants because it costs them less to heat their units. Lots of permutations you can figure.

Hope this helps!

Brad

Greg_34

Thanks Brad, I just downloaded the report. I'll give it a read tonight.

I haven't yet installed anything, so now's the time to do the research. Thanks for your input, I'm sure I'll be reading more into this and posting more questions.

In the meantime, who manufactures the 2-tier baseboards?

-Greg

siggy

baseboard lengths

Several years ago I developed algorithms to track the performance of fin tube baseboard as a function of flow rate, entering water temperature, and ambient air temperature. These are used in the Hydronics Design Studio software module named "Series Baseboard Simulator"

While it doesn't show exactly what happens with outdoor reset. It does allow you to size up to 12 series connected baseboards using a wide variety of boiler outlet temperatures.

BTW, I also support the idea that outdoor reset of baseboard systems is not only feasible, it's an excellent way to improve the comfort and reduce the "ticking" noises in many conventionally controlled BB systems. Glad some more published information is now available on this.

grindog

ticking baseboard

I am glad that you mentioned that . Every customer i have that we put outdoor rest on their boiler has told me that the ticking has gone away and the lower temps seem to make the house more comfortable.
One woman thought that the ticking sound was supposed to be there and thought i did some thing wrong to her boiler.

Greg_34

Interesting point

So, Grindog and Siggy, what boilers have you installed with the outdoor reset? And were any alterations necessary with the baseboard or the curves as Brad mentioned above? What were the results??

I was just reading up on a Munchkin boiler with the addition of an indirect for Domestic? I'm replacing a single pipe steam system and haven't put baseboards in yet, so I need to fill my head with some accurate information.

Thanks for any help you can offer.

Cheers

Mitch_4

2 tier baseboard

ARGO panel trim is available in 2 tier

Brad White_9

John

As you know, I enjoy your HDS program and it is especially useful for 'forensic' diagnostics of an existing system. By changing the supply temperature I wonder how that might play out toward spot-checking reset at at least a given point. Another module feature in the works I am sure!

I think a lot of engineers, myself and perhaps yourself included, took the notion of reset for BB radiation as wishful thinking at least at first. I think I have the study in .pdf format and will e-mail it to you if you do not have it already.

Brad

Brad White_9

2-Tier Baseboard

Argo comes to mind, and is about nine inches tall. Slant-Fin may also have such a model but I am not sure.

BTW: I have done other houses, more custom, with multi-tier baseboard behind cabinets and bookcases as one feature.
Just elements and hangers with architectural enclosures inherent to casework you would install anyway.

Toe-space air inlets and a really tall "chimney effect" behind the casework with outlet grilles on top. The chimney effect appreciably increases output for elements that are otherwise equivalent. Having a warm air film at the walls, even behind a bookcase essentially cancels out the heat loss too. One may argue it can increase heat loss due to increased Delta-T, but no one has complained yet.

Just some thoughts...


Brad

Brad White_9

Sorry Mitch

I did not see your answer before I posted. Argo and yes Panel Trim is the line.
BEW

bob_34

landlord strategy

i have installed a weil mclain ultra this year in my 3 family house with 6 zones of baseboard that i had already. i noticed the boiler condenses pretty well in the shoulder months when the outdoor reset tells the water to be 90 -130 degrees delivered to the baseboard. this gives tremendous efficiency over the non condensing temperatures from 130-190 during colder weather. i wish i had more baseboardin total footage or higher capacity per foot so i could enjoy more condensing/savings. however, i plan to install replacement window which typically save 30 per cent on heat bills which is the same thing as installing 30 per cent more baseboard radiation.

bob_34

landlord strategy

i have installed a weil mclain ultra this year in my 3 family house with 6 zones of baseboard that i had already. i noticed the boiler condenses pretty well in the shoulder months when the outdoor reset tells the water to be 90 -130 degrees delivered to the baseboard. this gives tremendous efficiency over the non condensing temperatures from 130-190[supply] during colder weather. i wish i had more baseboardin total footage or higher capacity per foot so i could enjoy more condensing/savings. however, i plan to install replacement window which typically save 30 per cent on heat bills which is the same thing as installing 30 per cent more baseboard radiation.

Greg_34

Argo

I took a look at the Argo panel trim. Looks good. One question though. The BTU ratings only go down to 150 degrees. Are these values reasonably linear so I could estimate a curve for lower water temps of ~120 or 130, like we discussed?

greg

Greg_34

Thanks bob

I didn't see your post until now. I'll take a look at that boiler. I'm looking for direct vent boilers because my chimney is pretty old and not drafting well.

Also, what are you doing for domestic hot water?
-Greg

Brad White_9

Generally, yes

Greg, you can extrapolate downward. It is more linear with radiant at the lower temperatures, but convective flattens a bit. Radiant output is fairly proportional but when the unit is convective, you have to have enough heat transfer to air to get the air to move by buoyancy.

In other words, to achieve perceived comfort you sometimes have to have a higher water temperature than for other kinds of emitters at the low end. (Even if they all start at 180 and go down from there.) Experimentation is key.

To extrapolate, plot out from what you know and see how she looks. The basic premise is proportional to inlet (or average) water temperature and incoming air, but the limitations will become apparent.

By the way, you did notice how the second tier only adds about 30% right? Not sure if that is with the top tier being the supplied tier and the bottom being the return. I think you should do that, definitely.

Greg_34

top tier/ bottom tier question. If I have one zone in a loop, won't the top-tier (supply) become the low temp return as it completes the circuit?

Or, do I send the water out to the furthest point and then u-turn it back to the boiler? I know what I'm trying to say here but my prose may be somewhat convoluded.

-Greg

Brad White_9

If

the flow path is a "U" on it's side, the top tier is supplied and yes the bottom becomes the return. The principle is that at any point you will have "Average Water Temperature" for the circuit. (Starting you enter at say 180 and leave at 160, you have a 170 AWT. At the return bend, halfway through, you should be similarly situated or a tad higher. Not exactly but you get the idea.)

If it is all "feed at one end, return at the other" (parallel flow) you can still pipe it in parallel but you might lose velocity and turbulence necessary for good heat transfer at low flows ("laminar flow"). If that is the case, see if you can get 1/2 inch tube element to keep the velocity up.

Did I get your question correctly?

Brad

grindog

munchkin

> Okay, that makes sense to me know. Initially

> with baseboards, i was anticipating the

> installation of a loop. Top tier/bottom tier

> under those circumstances would make the end of

> the loop very cold. The U-shape, supplying the

> avg. water temp makes sense with the install.

> The argo's look good, now I just need to figure

> out what systems would be correct. Based on

> Slant/fins software, my unit has a combined

> heatloss around 65,000. How much overrating is

> allowable before the system gets

> inefficient?

>

> -Greg

grindog

munchkin

we have done munchkins. They are a great boiler and easy to work with. The last job we did was a house with existing baseboard. The heat loss we did came out to about 110,000 btus and the existing boiler was 300,000 btus.
With the vision one controler the house heats up and runs great with 150 degree water, customer is more comfortable than ever and sleeps thrue the night with no noise.

Brad White_18

When you say over-rating

do you mean on the heat loss side or on the system side? Not sure what you mean. We may want to post this part of the thread further up the tree. We are going vertical here!

Brad

Mitch_4

no sweat..

Ihave done it too..no biggie. Even wrote a reply once and had someone else post the same info at the same time.

Happens. Knowlege is all about sharing

clammy

slant fin 80

I have done this with a munchkin m80 using slant fin 80 baseboard .I performed a heat loss on th e home and sized my baseboard for 160 water at desing day 10 ouitside 70 indoor and this system very rarely see supply temps of 160 except when at design temps .The home is very comfortable no noises and it runs at just about constant circ evn though it is 3 zones it also modulates down quite well to bad htp didn't have a indoor sensor to really bring it all together on another note from there old steam system there gas bill was cut in half and that was with about 1000 sq ft living space added and fair sized garage with radiant heat in the slab .It doers work you just have to run the numberes and make sure the home is well insulaeted and you can meet your heat loss with the proper amount of element and lower water temp peace and good luck clammy

John_82

Constant circulation w/ outdoor reset is the way to go. Let the pump rip & use danfoss style thermostatic operators for comfort control in each room. That way if grandma wants it hot in her room, she can do so with out burning the rest of the house up! When spring comes, the system goes into warm weather shut down & shuts down. By having constant circulation and reseting the temp to whats going on outside the house will be comfortable & economical!