Prestige with 8 spot manifold and constant circ??

Bob Bona_4

place to get info! I'm always learning too, and could listen to TRV design by others for a while longer...

Till my eyes glaze over, that is (G)

Jason_29

Prestige with 8 spot manifold and constant circ??

I've decided on the Prestige with Phase III for our replacement boiler. Now I just have to decide on whether or not to lose the diverter tee setup and replace it with a manifold and constant circ with trv's.

I'll be replacing cast iron with 8 flat panels for a total of about 30k btu. I've been told that the Prestige will handle being piped directly into an 8 spot manifold with a pressure diff bypass valve. Watts makes a nice manifold that accepts their own bypass right on the side opposite the supply and return. Taco and B&G make bypass valves too.

Is this the best decision? Will the bypass handle the constant circ if none of the trv's are calling for heat? Or should I use a low loss header (I saw one from TT in a piece of their literature) and a secondary pump. But that way, it seems that I'll have two pumps running all the time.

Also, if I use a thermostat that sets the nighttime temp to 62 down from 70 or so is that cool too?

Thanks in advance for your opinions.

Jason

ALH_4

LLH

I like that strategy a lot, and have done it with Vitodens boilers. I would not use primary/secondary piping in your situation. I would recommend using a separate dP bypass valve for an application like this. The only problem I can see is that the Solo 110 is quite oversized for a 30k design load. The 110 will be oversized even when the boiler is at low fire and your heat load is at its greatest. Therefore you will not be taking advantage of the modulating burner at all. However, this will be true of most boilers available, and there is some debate as to how much less efficient the boiler is under these conditions. A buffer tank may help with short-cycling.

Triangle-Tube also offers their Delta combination water heater/space heating units. However, I have no direct experience with these units. Perhaps someone else has used them before.

Why replace the cast iron radiators?

Mike T., Swampeast MO

First, I'd think long and hard before replacing the cast iron rads. I know they're big and clunky and some consider them hopelessly old-fashioned, but they're exceptional heat emitters. My best suggestion is to use the TRVs regardless.

The replacement panels [probably] won't have near the heat liberating capacity of the iron rads they replace. This will allow the iron rads to heat the space at a lower temperature than the panels. With a mod-con the lower the higher the efficiency.

Unless you pipe things with virtual drinking straws, the Prestige (or nearly any mod-con for that matter) should have zero problem being directly connected to your system with TRVs--iron rads or steel panels. The exact purpose of the differential pressure bypass is to prevent problems when all of the TRVs are closed.

My views of daily setback with mod-cons (and especially with TRVs) are a bit unconventional. Remember--you can set the TRV is EACH space to maintain the minimum temp suitable for comfort given the typical use of that space. Once you get used to TRVs, I suspect you'll find there's little need for much (if any) daily setback. Adjust the reset curve of the mod-con to be just a bit more than needed by the space with the highest temp requirement and I suspect you will find also that leaving the TRVs alone (saving unusual circumstance) results in nearly identical (if not slightly lower) energy consumption compared to daily setback.

The best way to use daily setback with a mod-con and a TRVd system is via supply curve setback--not by setting back the TRVs themselves (or any "master" thermostat). The Prestige [might] have this function--I'm not sure. Use the TRVs for constant setback of a rarely used space. Use any "master" thermostat for setback of the whole house for days--preferrably in conjunction with setback of the supply curve.

Mike T., Swampeast MO

Forgot to Mention

As Andrew stated, 30 mbh (assuming this is your design load) is unfortunately quite low for most mod-cons available in North America.

GIVE US SMALLER MOD-CONS!!!!!!!!!

Jason_29

Oh, I've thought...

long and hard about replacing the cast iron. We've got them in our house now and I love the heat and the efficiency. The new house is TINY, and the rads take up a surprising amount of floor space. They have been painted and would have to be refinished or covered and a few of them need to be repositioned. Plus we really like the look of the Runtal or Myson 2,3 or 4 tube rads.

I've oversized the panels so we can run lower (160 degree) water through the system, so maybe that will help with the efficiency of the mod/con. Plus we're considering an addition in a year or so that will add another 350 sq ft and 8k or so in loss.

The bypass capacity of the Watts valve is 9 gpm which is (I believe) more than I need in btu. Will the circ be ok with that?

Also, I've followed other posts about lower heat loss and mod/cons. Is there another option? We're replacing a 165k btu NewYorker.

Thanks again,

Jason

Paul_37

smaller MOD-CONS

I would use the Munchkin 50,000 Contender

Wayco Wayne_2

I agree with Paul

Size the boiler so you can stay within the throttling range of the boiler. I was going to mention the controls option in the Prestige that alows you to reset the outdoor reset curve down whenever the thermostat isnt calling so you don't turn all the way off and can keep your constant circ and set your outdoor reset as low as you like. I like it cuz you can keep on heating somewhat and not lose the heat completely like an air sensing set back can let happen. Keep some heat in the thermal mass of the walls while you're saving money. WW

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Steve Ebels_3

Agree also

The Prestige 110, while being a very nice piece of equipment, is waaaaayyy too large for your application. If your heat loss is truly only 30Kbtu at design, you'll find yourself in the position of adding a buffer tank or letting the boiler short cycle itself to death. Something with a max firing rate of 50K would be more like it for your use.

Uni R_3

Recommendations

- ditch the monoflo to widen the ΔT/lower the return temps

- if you can't keep the cast iron, size the panels for 140° max

- get the prestige, it will not short cycle

- pipe it direct to the manifold but widely spaced from the boiler

- the space is for p/s if you ever need a second temp circuit

As for temperature control you'd have 2 main options. You can go pure ODR - the boiler will be constant circ only and the water temp will be targeted to what YOU say it should be at the current outdoor temperature. Your comfort will be as good as your curve settings and the sensor location. My sensor was very sheltered, the house would always be cooler the first day when a cold front would blow through. Shooting the sensor location with a temp gun gave me that answer, the bricks there were sheltered and holding about 4° higher. Multiply that by the slope and it also shows why it's 66 in the house instead of 69. Anyway. It's doable, and its as good as the sensor location. Mine's gonna be relocated and hopefully even get a bit of solar gain. You can even do programmed parallel curve shifts using any simple programmable t-stat. It checks to see whether of not it is getting the on signal and this determines whether or not the curve (water temps) all get shifted down by X degrees. The MCBA has no clock function, the t-stat in this case merely works as a scheduler.

For a true kiss/t-stat design, use a t-stat in one room without a TRV. Calculate the velocity using the internal 15-58 on low using just that radiator with the full flow. You may not even need a ΔP valve for one and doubtful if 2 had no TRVs. I'd also try a 20 minute post CH purge rather the constant circ. I can't feel the difference on my lowly HWBB and I should if it costs money.

Anyway... it's not hard to change either way between the above 2 options.

Just don't rule out the Prestige for it's lack of bottom end modulation. I have one and my load isn't enough to make it modulate. There still isn't a boiler on the North American market I'd rather have and can make DHW in spades.

Don't listen to any bull about it short cycling. It fires 10 minutes at a time. That means 5 to 6000 total BTUs being dumped into a circuit over a 10 minute period. If there isn't enough load and/or water in a circuit to handle a small charge like that blame the designer not the boiler. The Prestige in this case would hit the temp limit for the curve and wait a very long time before firing. Hardly short-cycling.

Anyway, ditch the diverter tees and if you go panels, get the temps dropped below 140° and your energy bills with the Prestige will be very far out into the land of diminishing returns to go much lower.

Unless the boiler has some huge unknown flaw that has yet to be exposed, I can't see there being any downsides to going with the Prestige.

Uni R_3

Steve

"If your heat loss is truly only 30Kbtu at design, you'll find yourself in the position of adding a buffer tank or letting the boiler short cycle itself to death."

Steve, have you ever personally witnessed a Prestige short-cycling? My heat load is too low for my Prestige to need to modulate. It never fires for less than 10 minutes.

BTW, the maximum efficiency is there on low fire and the sound is as quiet as it gets. It doesn't modulate and it won't short-cycle either - I see no downside to the Prestige for this application nor any reason for you to scare the purchaser here.

Jason_29

Uni,

Thanks for the detailed advice. The Prestige is attractive because of the ease of installation and the stellar reviews on the board. I like the stainless construction too.

I'm a bit of a techno geek and I'm looking forward to tweaking the system to have it run efficiently on its own. Is the 140 temp as high as I'd want to go? The rads start to get big at 160 I'll have to recalculate for 140 and hope that they're not too massive.

I like the idea of using one or two panels without the trv's and use a tstat in that room too. Is 1/2 inch tubing too small for the home runs?

Thanks again for your help,

Jason

Uni R_3

Diminishing returns...

Jason, it's tough to just grab a magic number because for every degree you lower your system, the marginal cost of the rads increases (the have to get bigger exponentially) while the marginal savings through cooler returns decreases (especially under 130°). Just how much the savings change as return temps drop isn't something that can be easily calculated in advance as far as I know. I've never seen a good load/return temp efficiency chart that was done by an independent neutral party so to me this aspect is more assumption than math.

Even sized for 160° supply temps, the return temps would probably still be in the condensing range all but a few hours or days per heating season, but I'd still try and justify the extra bucks for the larger rads to get that efficiency to a near ideal state. Fuel's only going to get more and more expensive as world demand outstrips supply.

At some point it's just not economical to try and lower the temp any more. My thoughts on 140° supply are this. Between heat loss calculation errors and the fact you might only hit that supply temp a few times a season, over 99% of the time your return temps will be under 125° and in the 100° range or less for the shoulder seasons. BTW, that's also pretty close to the required temps for underfloor heating with plates if you ever want to add radiant but keep it all one temp for simplicity.

Bigger rads also give you better recovery options when you come back from a trip and want the house back up to temp quickly.

As for pipe sizing, you have to consider the load and piping length for each rad and whether or not it has a TRV? You want to keep the velocity down to a silent level (>4fps) when all the TRVs close and the t-stat rad(s) is getting the full flow. I'd do those calcs assuming speed 1 on the 15-58. Using speed 1 will keep your electrical consumption extremely low. The controller takes 14 watts at idle and about 85 watts total when heating (that includes pump, fan and controller) which would work out to about $50 a year at 15¢/kWh.

I'd think that ½" should be fine but these actually are numbers that can be very accurately calculated by you or your contractor unlike trying to size the rads for optimizing the ROI which is much more of a guess.

Eric_36

Valves

> I've decided on the Prestige with Phase III for

> our replacement boiler. Now I just have to

> decide on whether or not to lose the diverter tee

> setup and replace it with a manifold and constant

> circ with trv's.

>

> I'll be replacing cast iron

> with 8 flat panels for a total of about 30k btu.

> I've been told that the Prestige will handle

> being piped directly into an 8 spot manifold with

> a pressure diff bypass valve. Watts makes a nice

> manifold that accepts their own bypass right on

> the side opposite the supply and return. Taco

> and B&G make bypass valves too.

>

> Is this the

> best decision? Will the bypass handle the

> constant circ if none of the trv's are calling

> for heat? Or should I use a low loss header (I

> saw one from TT in a piece of their literature)

> and a secondary pump. But that way, it seems

> that I'll have two pumps running all the

> time.

>

> Also, if I use a thermostat that sets

> the nighttime temp to 62 down from 70 or so is

> that cool too?

>

> Thanks in advance for your

> opinions.

>

> Jason



Jason,

Eric_36

Valves

Jason,
Check out the FPE valves to go on this system. It is a great valve for maintaining system temperature and nearly eliminates typical boiler condensate and thermo shock issues. Look at their site: www.fpevalves.com
I think that this is the valve for your system. Keep us posted. See ya.

Steve Ebels_3

OK OK

So I get a little ostentatious with the hyperbole .............occasionally.................once in a while............sorta. I apologize.

How about this statement.

Although the Prestige holds about a gallon and a half more water than some M/C boilers, helping to reduce short cycling, the fact remains that its minimum firing rate of 30,000 btu is your maximum load. This means that the only time your boiler will operate at a steady state is when you are at you coldest day of the year. This is not a desirable system characteristic for any boiler. That being the case I would humbly suggest that you search out methods of lengthening the run time of the Prestige or select a boiler that more closely matches your load.

Izzat better?

Now sir, could you explain what this statement means....... "My heat load is too low for my Prestige to need to modulate.".....So, if your heat load is too low to modulate then it must be cycling on/off. Right?

Uni R_3

No probs...

Part of the explanation is that my minimum firing rate is actually around 38 - 40K according to many many clockings. My heatloss turned out to be around 38K, not 56K as per Manual J, nor my more conservative estimate of 45K. I ignored considering this boiler for a year because of the 30K minimum, so I was very much aware when I decided on it.

My heart was set on the Ultra 80 and I think the biggest reason was the 16K minimum. When I called W-M to get names of installers they would recommend, they told me me "They believe in the wholesale model". They wouldn't give me a name! I only found one guy in a 5 million person metro area and have to thank Dobber for that lead, but this guy hadn't installed one in a few years and was always hard to get ahold of and rescheduling.

Viessmann was very responsive when I called them. They gave me a couple of names and along with details on the Vitodens 100 that I wanted to know before committing to anything else - this was back in October or so. Unfortunately, I wasn't crazy about the complexity on the Vitodens nor the knowledge of either of the Viessmann installers (the first guy told me right off the bat I needed an 8-32 not a 6-24 and that the coax couldn't go far enough up the abandoned chimney - it can 33' max) and the second guy kept blaming Carrier for delays in him getting pricing - he took weeks and then wanted 6K extra for the little 53gal horicell 300.

I had cold feet until I called T-T Canada. The guy they suggested I call first ended up installing my boiler - they were even black iron specialists. Everyone else was copper which I didn't want for main piping since everything was already black iron.

***** ***** *****

Every single modulating boiler cycles or pulses above a certain outdoor temperature. For this situation, it was supposed to be the freezing mark. But with the lower heat load and reduced modulation range (top end still clocks around 110K), modulation doesn't occur until design temps or lower. If it could get down to a minimum fire of 30K, then anything under 10° would have it modulating.

I do wish my boiler modulated down to it's advertised minimum, but I'm still totally satisfied and there isn't a boiler on the market that I'd trade it for except maybe an ACV Prestige 24 (20-80K).

As for the extra 12 pounds of water in the HX, I don't think that is much of a factor in absorbing excessive BTUs. P42 on the MCBA controller on a Prestige is what ensures each firing of the boiler lasts a minimum of 10 minutes. You can also program minimum times between firings if that isn't enough.

***** ***** *****

Given the original poster's situation and my experience, I really do think it's still a good match. Actually with the right t-stat and 1½°s of setback, this is what the total energy consumption picture looks like. This graph shows the electrical consumption for March 7th, 49 HDD. 14 watts means it's off, 98 watts is that it's firing and running the pump at speed 2. Those are pretty nice cycle lengths if you ask me.

The March 3rd graph shows it on firing 10 minutes at a time and then varying spaces in between. In this example, the old t-stat was still calling but the boiler would '6' out on the reset curve - this is as bad as it got and I'll bet that most homeowners wouldn't even know this was going on unless you were sitting in front of the boiler for hours on end. ;-)

Jason_29

Thanks again for the input. This is getting down to a fish or cut bait situation. Just when I think I've gotten it down, more consideration is required. It's been really interesting hearing from people who are obviously professional heating contractors and others who are seemingly not. That's why I love these boards.

I totally understand the ideal of sizing. My heart says go with the Ultra 80 or the Knight or Buderus all of which fire lower than the Prestige. My head likes the simplicity of the Prestige.

It's been really difficult to find anyone locally interested in installing a mod/con. There are lots of old school companies around that don't even want to look. I did, however find an installer on this board who is knowledgable and enthusiastic.

As long as I'm basically starting from scratch, I just want to have the best (performing and efficient) setup that fits my budget. My wife is probably going to finally tell me to stop ruminating about it and I'll probably do the whole house in fintube

Thanks again,

Jason

Bob Bona_4

yeah, would you please?:)

Don't forget Jason, you need decent BTU's to get the indirect to recover in a reasonable amount of time. That's part of the quandry re: house load vs. domestic. Guess a little short cycling has to to take a backseat to recovery. I suppose we could add a buffer tank if we had to down the road..if you can find a spot for it..

You'll be fine with 1/2" risers to your emmitters- whichever you chose. I wonder if that 9 gpm dp valve would hunt with it's size. I can check out Wirsbo's setup for the Propanels and see how they spec it.

If you wanted constant circ w/ TRV's I think you'll have a pretty even load with the house it's size..no long halls, isolated wings..the TRVs will near mimic each other.

This is your chance to zone the second floor, you know that right?

Jason_29

See that Bob? I'm trying to take the heat off of you a little and this is the thanks I get. Better suss it out now than second guess myself (and the installer ) later!!

Jason