Any downsides to oversizing radiators?

SWEI

Sorry -- forgot they had more than one SR501. You want the SR501-4.

Gordy

Keep in mind that the indirects capacity is based on the SWT, and flow rates. Anything less you gotta up size , or be disappointed in recovery. Your not dealing with high usage I don't believe so once indirect is up to temp your probably good with initial draw.

P/s piping will ensure the boiler always gets it's flow rate, the indirect will get it's required flow rate, and the emitters will get theirs which will be variable depending on the trvs position.

You will be much happier going with ODR in the installation. All though the boiler is only going to be 85% efficient no matter what. But the comfort level will be increased.

If you rewind to the beginning with your initial question with over sizing radiation. What it does in respect to high efficiency equipment is allow those return temps to get down to condensing range where more savings will be realized. So instead of 170 AWT you would try to get down to 140 awt or lower to get into condensing mode, and pick up a few efficiency points on the boiler.

Sometimes radiation is oversized as is do to envelope upgrades, or initially they were oversized to begin with through installer error, or playing it safe ( no one complains so long as their warm). Your starting from scratch.

The whole idea with ODR is to have just hot enough water to off set the load. Not bang 180 cold soak bang 180. More of a mellow unnoticeable constant ambient.

If your thermostat is just a high limit, and the trv's are your temperature control they will be mostly open I believe with odr. Keep in mind once this is all put together there will be a period of weeks to fine tune the reset curve to get to that point.

alheim

Insightful as always.

I am struggling to find the definition of "SWR" in relation to indirects? Supply Water Temperature? The Amtrol BoilerMate indirects, 41 gallon, seems to be an easy choice (specs below).

Yes, so in the case of my atmospheric boiler, there is no significant reason to oversize the radiation, as there is no condensing mode. If in the future, however, I move the boiler upstairs out of the flood zone for an insurance reduction + boiler safety in case of another flood (unlikely, but an option), oversized rads would help if I switched to a mod/con. I don't yet have an upstairs location for a boiler, I would have to build it. I may oversize emitters by ~20%, and that will increase as I tighten the envelope. I'll include thermoters on supply/return. If return water temps get low, I'll add a mixing valve or thermic valve or bypass loop/valve.

Thanks.



Link to brochure: http://www.amtrol.com/media/documents/boilermate/MC10164_06_14_BoilerMate_Brochure.pdf

Eastman

@alheim I want to reiterate what Gordy said, "advice was given on a tight budget" --I would suggest other configs for different budgets and wishes.

Regarding the schematic I posted: This design was a first attempt at creating the best compromised solution for you --with the problems being, in my opinion: a)Where is this system going to store the fixed 60k output from the boiler?? And b)How is it going to unload the energy in a useful way. Mixing valves, TRVs, ODR, etc., are great at correctly distributing even heat but prevent thermal storage in the emitter system. Relatively speaking, I would be concerned the boiler would be boxed into frequent cycles with a system combative high differential unless some means of thermal storage is provisioned.

The indirect thermal storage diagramed, is an attempt at creating a solution to both thermal storage and tempered output for both the boiler return and system supply.

Given the desire for TRVs, I would think such a setup would afford you the best odds for avoiding or delaying the use of ODR, mixing valves, boiler low temp protection, and DHW priority.

@Gordy regarding boiler low temp protection: With parallel flow, it seems unlikely the boiler would be exposed to temperatures below 110. I think most people would stop taking a shower if it started to feel cold, e.g. When you think about it, the boiler is one of the cheaper components in this system, and I feel a knowledgeable homeowner might consider managing such risk if it was mitigated in a predictable way.

@Gordy regarding the pumps: The flow at that location is the addition of boiler loop and system loop, so one probably needs something to handle approximately twice the design flow to the emitters, and I kinda wanted to keep 5/16 dia. tubing in play.

@Gordy regarding "If an indirect was in the budget how would it see high enough supply temps with return water mixed with indirect supply water? Especially with ODR?" A TRV'd system should only dominate the mixed down boiler output as the system approaches design conditions. If using an ODR, the setpoint should be at its maximum for this condition, and assuming reasonable deltaT's, the mixed boiler output into the indirect would be very hot and constantly running.

Paul48

I think my head just exploded...

Gordy

I'm not sure what the obsession is with 5/16 pex the pressure drop is quite a bit more than 6' of head for 125' at .30 gpm... That's a lot. It was designed for viega climate panels.

I'm sure his home runs will not be long, but 3/8 is quite doable for the btu requirements, and flow rates with lower head loss. This would allow the alpha to save more energy. Also in my mind pipe with larger volume allows less of a temp drop before it gets to the emitter.

Remember the boiler has been selected. The initial concern is lower than 110 return temps. To me the simplest solution to prevent that is the 4 way valve.

The most excepted solution to cycling will be a buffer tank. You can't depend on an indirect as the buffer in all situations at all times. How will you control the indirect calling when the temp,drops on a heat call, and your pulling btus off the indirect by not having domestic priority right.

I just don't think there is any savings or at least a wash in boiler cycling verses an indirect calling solely because it's temp was pulled down by a heat call do you?

alheim

I came across this piping diagram - the indirect comes off of the supply header, and then a 4-way mixing valve is used to protect the boiler, and to modulate the water temp to the emitters:



From here: http://www.radiantandhydronics.com/articles/86257-mixing-valves-boilers-and-radiant-panels

It cuts out a circulator compared to a P/S setup (2 vs 3). The 4-way has a supply temperature sensor & a boiler inlet temperature sensor.

Gordy

Yes that will work use the I valve with outdoor reset, and your done forget the card.

Eastman

Keep in mind, that the "low temperature distribution system" in that diagram is a probably code for something that has a lot of thermal mass, like a slab, and would be buffering the output from the conventional boiler. Are panel rads that see only mixed ODR water capable of storing much energy?

alheim

@Eastman isn't that where the 4-way comes in & protects the boiler regardless of the mass of the emitters?

I'll have something like 625' of 1/2" PEX to the emitters on the 1 zone. Plus, I can oversize the emitters a bit. (I have to place my radiator order tonight for them to arrive by Friday.)

4-way valves sure are pricey though; the Taco 4-way w/ ODR & supply/inlet temp sensors are over $500, slightly more than the ODR card which has DHW priority. And then I lose any efficiency that the ODR card might gain me - I think? Is that even significant with a conventional boiler?

Gordy

The I valve kills two birds with one stone odr, and 4 way valve for boiler protection all in one. The card does nothing to address low RWT. I don't see the dhw priority as a huge miss with small demands and fixtures. Remember that indirect will out perform a standard 40 gal WH.

alheim

Clearly I'm still confused on some of this but here's an easy question: how does an indirect call for heat? Assuming a plain-jane indirect w/ it's own circ.

Edit: another easy one: in this setup w/ the 4-way, do you just set the boiler output temp at 1 static temperature that works best for the indirect, and then let the 4-way handle the distribution to the emitters?

alheim

Again I promise before & after photos of all this. At the least. I don't know how to repay you kind strangers.

Gordy

Also in reference to your head loss calculation it's the highest head loss loop is all need to be overcome by the circ.

So from the supply header to the rad, and back that length .... The longest is what your looking for plus the pressure drop of the manifold, and associated piping from the circ location.

Gordy

Please refer to the I valve r piping instructions you still have to go p/s.

SWEI

Looks like one of Siggy's drawings. With the near-zero head loss in a conventional boiler, a 4-way valve will usually work without a separate primary circulator. You want short, full sized pipes and minimal fittings on the boiler side and you also need to make sure the valve never closes completely -- some designs have a hole or a notch in the paddle but with others you will need to drill your own. No idea how to size that hole, but somebody here probably knows.

Gordy

alheim said:

Clearly I'm still confused on some of this but here's an easy question: how does an indirect call for heat? Assuming a plain-jane indirect w/ it's own circ.

Edit: another easy one: in this setup w/ the 4-way, do you just set the boiler output temp at 1 static temperature that works best for the indirect, and then let the 4-way handle the distribution to the emitters?

The indirect is tied to the boiler control it has it's own aquastat. When it calls the circ starts ,boiler fires until indirect reaches temp.

Yes the boilers water temp will be set the I valve will mix system supply and return water to meet the load based on outdoor temps, and protect the boiler. Read the I valve r install instructions.

Eastman

@Gordy Smaller tubing looses fewer btus per foot for a given flow rate and initial temperature. Hence, the temperature would be hotter at the end of the run.

"I just don't think there is any savings or at least a wash in boiler cycling verses an indirect calling solely because it's temp was pulled down by a heat call do you?"

Surely, a system with more thermal mass and yet the same btu loads will have fewer cycles? I can't see it any other way. Granted there are some control details to iron out. A buffer tank is the norm, but what is the best compromise?

@alheim Low temperature thermal storage is capable of buffering boiler output but is not capable of low temperature condensation protection. Hi temperature thermal storage could be capable of both, hence the possibility of eliminating some protection devices. An I-valve can protect and distribute, but where's the thermal storage?

alheim

Thanks. I'm reading the iSeries-R (outdoor reset) valve instructions now. A link for those interested: http://www.taco-hvac.com/uploads/FileLibrary/102-145.pdf

Does using a 4-way w/ built-in ODR features compromise energy savings (because of the static supply temp) that you'd get from Burnham's ODR card, which modulates/dials down the boiler's system supply temp? ::

I'm guessing it's a wash. Two scenarios: 1. On mild days, with an ODR card you'd get longer boiler cycles at lower supply temps. 2. Or, with a 4-way w/ built-in ODR, on mild days you'd have shorter cycles at the usual 'higher' boiler supply temp, with the 4-way controlling emitter temp.

This is what @Eastman‌ is trying to say, isn't it.

The highest emitter is ~14' max above the boiler, and the longest loop at that height is about 65' loop.

Gordy

Eastman said:

@Gordy Smaller tubing looses fewer btus per foot for a given flow rate and initial temperature. Hence, the temperature would be hotter at the end of the run.

"I just don't think there is any savings or at least a wash in boiler cycling verses an indirect calling solely because it's temp was pulled down by a heat call do you?"

Surely, a system with more thermal mass and yet the same btu loads will have fewer cycles? I can't see it any other way. Granted there are some control details to iron out. A buffer tank is the norm, but what is the best compromise?

@alheim Low temperature thermal storage is capable of buffering boiler output but is not capable of low temperature condensation protection. Hi temperature thermal storage could be capable of both, hence the possibility of eliminating some protection devices. An I-valve can protect and distribute, but where's the thermal storage?

I think you need to look at the head loss of 5/16 pex verses flow rates. The cut off on the chart is .7 gpm that would be 13' of head in a 65' loop ridiculous he is up in the 1+ gpm with some loops. He's using 1/2 good choice.

My point about cycling is your preventing cycling through mass that is also supplying another function that's DHW. So your robbing from Peter to pay Paul because Paul wants to be ready to go when there is a demand so now Paul is,wanting some btus.

On the other hand a buffer tank is ready to go for one purpose heating. As soon as it's btus are depleted it's going to call if sized right after the heat call,is satisfied this will have latitude depending on tank temp,boiler temp, emitter temp for the odr.

Your banging 180 to the indirect every time it's depleted to get tank to maintain 140 or more then trying to draw off the tank temp to buffer the boiler with 140 via the tanks hx.

I think it would have substance if the indirect differential was wide enough to bring the tank temp down low enough for a long cycle in this case not so low as,110 return to the boiler is not maintained about that time someone's wifey wants a hot shower.

Personally I don't think cycling will be huge. This is where we talk about that other type of boiler that modulates.

Gordy

alheim said:

Thanks. I'm reading the iSeries-R (outdoor reset) valve instructions now. A link for those interested: http://www.taco-hvac.com/uploads/FileLibrary/102-145.pdf

Does using a 4-way w/ built-in ODR features compromise energy savings (because of the static supply temp) that you'd get from Burnham's ODR card, which modulates/dials down the boiler's system supply temp? ::

I'm guessing it's a wash. Two scenarios: 1. On mild days, with an ODR card you'd get longer boiler cycles at lower supply temps. 2. Or, with a 4-way w/ built-in ODR, on mild days you'd have shorter cycles at the usual 'higher' boiler supply temp, with the 4-way controlling emitter temp.

This is what @Eastman‌ is trying to say, isn't it.

The highest emitter is ~14' max above the boiler, and the longest loop at that height is about 65' loop.

Here is what I think if the boiler is off it's not using any gas. Cycling does effect efficiency if the boiler is not on long enough to get a stable burn 10 minutes usually, and there is component cycling. Trying to make the boiler run longer to create mass for the next call just seems like a wash unless,the boiler was extremely oversized for the load.

Hey I have been wrong before.

alheim

I am thinking & will continue to think about the piping for the next day or two.

My immediate concern the sizing the radiators, as I've got to get that order in now, so that the warehouse can pallet the rads and ship them off to me in time.

Can I ask you gentlemen for some consensus on this? Back to post #1. Will I regret oversizing by, say, 20%? The cost is minimal. (Some examples below.) It seems that in most piping scenarios that we've discussed that we'll be able to protect the boiler.

Assume an indirect. I am going indirect for sure.

Let's not talk about that other type of boiler. That cutting-edge type that we all like and that the OP shunned, probably incorrectly.

Eastman

Oversizing: Takes up more space, that's the disadvantage. Is cast iron a lot more expensive?

alheim

^ Yes, all the CI emitters that I'm seeing are quite expensive - prob another $2,500+, and I'm not sure of availability. The panel rads seem like a nice modern take on the old CI rads - just as good if not better at getting heat out per unit of space - they just don't have the iron mass to hold heat as long.

I know, it does seem silly to 'oversize' at all - why spec something that doesn't match my boiler.


Using the combined living room in hall space as an example: 8,630 + 2,939 = 11,569 BTU between 2 rads = 5,785 BTU/hr/each. The 22 series rads are 4" thick.

A 19-5/8" tall by 35-3/8" long unit outputs 5,926 BTU @ 180°F (already 2.5% oversized at 180 degrees, about as close as I can get). This holds 1.24 gallons of water.

If I oversized by 20%, I'd be looking for unit outputting 6,942 BTU @ 180°F. So I'd buy the 23-5/8" tall by 35-3/8" long unit, outputting 7,177 BTU @ 180°F. This holds 1.44 gallons of water (only 0.20 gallons more than the non-oversized unit).

I know I am using the word 'oversized' wrong - it is only oversized if we're assuming 180 degree water.

Here's a new way to put it: what target water temp could I aim for on design days?

alheim

Just for the forum's use, here's a link to the radiator tech manual: hydronicalternatives.com/getattachment/9b1601b5-feb9-4c69-9840-2977e2632afe/New-document-%281%29.aspx
General overview: hydronicalternatives.com/getattachment/6776700b-abbc-47c4-8f7e-f1dc5fbe1678/New-document.aspx
Stock price list: hydronicalternatives.com/getattachment/d4b8de2c-a220-4ea1-9286-0b8d5f819d6b/Stock-Flat-Steel-Panel-Radiator-Price-List.aspx

Eastman

Where do you see the output for 180? Is that an average of 200/160?

alheim

Yes, 180 AWT.

This document contains the correction factors for lower water temps: hydronicalternatives.com/getattachment/bd2181ec-c859-4344-8ffa-e0ce0a282be3/Correction-Factors-for-Low-Temperature-Hydronics.aspx

alheim

I forgot mention this, even with all the talk of bypass:

The radiator salesman suggested using these diverter valves with the panel rads (photo follows). They allow 35% flow through the radiator and 65% through the bypass. I feel that these are intended for having the rads in a series instead of in parallel (home run).

Diverter:


I was leaning towards using the regular isolation (non-bypass) valves. But it's something to think about.

Isolation:


(They both come either angled or straight.) These also function to adapt from British pipe thread to NPT, or PEX/copper (compression).

Eastman

Is there a more expansive design manual? That data seems to assume a 40 degree delta with a 200 degree supply.

alheim

Yes, it's here: hydronicalternatives.com/getattachment/bd2181ec-c859-4344-8ffa-e0ce0a282be3/Correction-Factors-for-Low-Temperature-Hydronics.aspx

Gordy

alheim said:

I forgot mention this, even with all the talk of bypass:

The radiator salesman suggested using these diverter valves with the panel rads (photo follows). They allow 35% flow through the radiator and 65% through the bypass. I feel that these are intended for having the rads in a series instead of in parallel (home run).

Diverter:


I was leaning towards using the regular isolation (non-bypass) valves. But it's something to think about.

Isolation:


(They both come either angled or straight.) These also function to adapt from British pipe thread to NPT, or PEX/copper (compression).

Yes you are correct that would be if rads were piped in series. The valve would allow water to bypass as TRV is closing so other RADS down the line get flow.

Gordy

Eastman said:

Is there a more expansive design manual? That data seems to assume a 40 degree delta with a 200 degree supply.

Its still 180 AWT. Across the pound they tend to use wider deltas nothing wrong with that its still AWT.

Gordy

http://www.heatlines.com/downloads.html

Thanks Carl. This will enlighten you there is a conversion factor table for different outputs at differing water temps.

Eastman

Yeah, I found the low temp correction table. I would knock the AWT down by 20 and look at 40 and 20 degree deltas. See what kind of correction factors you get. For example, 180 supply 140 return needs a 1.29 correction at 68 degree room temperature. 170/150 --also 1.29. What about 170 AWT at 40 and 20 deltas? (40 delta corresponds to 190/150 and is not on the chart) 180/160 has a 1.13 factor.

Eastman

Some things to consider beyond efficiency: upsizing can help with setbacks and reduced flow requirements. For example, a room on the end of a long pex run that needs to recover every morning from setback could benefit by maintaing high output at reduced flow from the extra resistance.

Gordy

Setbacks do not Marry well with outdoor reset forget the setbacks! It's counter productive.

Eastman

Let's see --what does everyone agree on....

Low flow meters on the manifold.
No disadvantage to oversizing rads.
Some kind of boiler protection.
I'd go with pex-al-pex if you go with 1/2 inch tubing.

alheim

Gentlemen, the radiator order has been placed. I sized them for 170°F AWT at the outdoor design temp of 13°F and indoor temp of 68°F.

So, a mild 'oversize', or said more correctly, a reduction in supply temperature.

I will post a schematic of my intended piping diagram for criticism. Basically: Primary/Secondary (1-1/4" primary loop), with a 'smart' 3-way valve or a thermic bypass valve for boiler protection, with 2 secondary loops: 1 indirect hot water heater loop, and 1 zone of home-run'd TRV'd rads on supply/return manifolds w/ flow controls. Total 3 circs.

I'll use 1/2" Uponor "hePEX" which has an oxygen barrier.

I like the idea of the thermic valve on the bypass because it is so simple. The one that @SWEI suggested is the LK823 ThermoVar from Sweden, see: https://oilstoves.co.uk/webdocs/technical/Valves/LK823_TERMOVAR.pdf I'd get a 1-1/4" model set to open at 45°C (113°F). Maybe the 50°C (122°F) model for an larger safety margin.

Then, I can add the ODR card down the line if it seems appropriate. I can set domestic HW priority with or without the card.

alheim

Like so:



Link to schematic image here

Not sure if I've got the bypass valve in the right spot. Not sure about quite anything. Criticism welcomed.

Bob Bona_4

I would not use Hepex here. Pex AL pex is your friend. I also would not take the DHW off P/S...pipe it direct. Why have the primary pump run when it doesn't need to?