0-10v modulating boilers

DrPcFix

I'm about to replace my nearly 30 year old WM250 boiler with something more appropriate to my now fully insulated home in Long Island NY. In addition, I'm planning on ditching my separate gas DHW and getting an indirect tank.

Several years ago I reconstructed the house and put in 6" of foam into all walls and 10" under the roof. Performing a manual j calculation I get a need for a 100K BTU unit. This is corroborated by a gas usage vs degree heating days analysis for the past several years.

The home today has 9 zones of radiant and 5 Zones of high temp 2 are backup heat in ac coils put in just in case the radiant did not provide sufficient heat (it does). 1 is connected to radiators in two bedrooms and 1 is connected to a length of baseboard in 4 bedroom while the last goes to radiators in the basement (also not needed). Everything else is radiant with each room on it's own thermostat, all connected to Tekmar controls.

So, I'm looking for a new boiler which I can control the modulation with the Tekmar control which supplies a 0-10v signal. Many of the unit's I've looked at don't even have the ability to be externally modulated as they expect that their control is all that's installed.

Right now, I'm circling around the Lochinvar KBN-151 which is a tad too big but the next smaller size seems a tad too small. I'm contemplating adding a 30 gallon buffer tank to prevent short cycling.

My ears are open

hot_rod

The manual has some info regarding the inputs and outputs. The ramp delay is another nice feature, it lets you limit and adjust the output firing of the boiler.

http://www.lochinvar.com/_linefiles/KBII-I-O Rev O.pdf

Tinman

You may want to consider the WHN-110 as an option depending on which side of 100k your heat loss is? It has the FireTube heat exchanger also. Same control as the KBN.

DrPcFix

The 110 probably would do, but I'm so close to it's max range I'm worried that on a colder than design temp day there won't be enough heat. In addition, I made no adjustment for DHW needs and even on very cold days hot water will be needed. That's why I'm thinking of adding the buffer tank -- to soak up the extra output on minimal days. On new construction I'd say that a manual J calculation could be trusted 100%, but on a 75 yr old house which was upgraded over the years, I'm worried that it may need a bit more btu's.

hot_rod

Its a tough call these days, didn't the east coast have 2 weeks of below design recently? If that becomes a trend you don't want to size too much below, or exactly to design.

That's what I like about the ability to electronically derate that boiler. I mentioned Lochinvar, I suspect other brands have a similar feature.

With dozens of boiler brands and models, you should be able to hit real close or a tad over if above design conditions are a concern. Keeping in mind you need enough heat emitter to move the load.

It's always a bit of a crap shoot, understanding fudge factor in the programs, and getting an accurate load on an evolving remodel.

Tinman

I completely understand that concern.

Rich_49

So you have a wall R value of 30 and a ceiling or roof plane R value of around 60 . this takes into account thermal bridging . There must be alot of glass .

All that aside we all should remember out of 12 zones , the odds of all having a demand simultaneously is minimal . Also take into account the amount of circs this job has and the fact that many of these circuits will satisfy rather quickly leaving plenty of juice for the system without oversizing . I for one would love the ability to install smaller than heat loss boilers due to diversity factors such as this . We all know it works M.E has a 50K boiler in a 100K house for a long time now .

My suggestion , put in the right size boiler . A couple ODR mixing devices for the varying water temps . Split that manifold into low and high temp , get rid of those 14 PSC circs and use 2 ECMs and zone valves .

You have done extensive work on this house so a Man J should be close to accurate . I'd be shocked if this home ever required 75% of the 110's output at any given time .

Taking all this into consideration I don't think a 30 gallon buffer would be large enough either .

Paul48

I don't think youhave a sizing issue, as much as you have zoning (micro-zoning) issue. You're splitting 100 k/btus between 14 zones. After having the system in operation, for a while, you ought to be able to tweak those zones, and lose some?

DrPcFix

The reason for the zones is so that different rooms can be kept at different temperatures. Unoccupied rooms don't need to be heated all of the time for instance. Also, some zones have much more heat loss at times than others -- for example the front hall -- open the front door and the temp in that area falls rapidly. Having it's own zone means that it can recover quite quickly once the door is closed. The start of that loop for instance was placed right by the door just for that reason. Living room is seldom used so it's kept cooler than the kitchen where nice warm floors are always welcome. The master bathroom needs to be warm in the morning and evening but can be kept cooler the rest of the day. The master bedroom gets heat at night which drops off by the morning and runs lower all day. Heat in the dining room is only moved up when occupied which is rarely.

Low temp zones are already regulated by their own zone injector pump. Each zone pump is set for optimal flow for that zone. Some zones have two loops while others have three or four. Some are on the 1st floor while others are on the 2nd.

I calculated a 30 gallon buffer by taking into account a 20 degree change in the buffer tank between fires of the boiler. In actuality, my control will vary the differential from 21 degrees (when it's warmest) to 1 degree when it's coldest.

30 gallons x 8.33 lbs per gallon x 20 degrees = 4998 btu's. The boiler on minimum fire is capable of 30k btu/hr so this would equate to about 10 minutes of running to bring it back up or at most 6 separate fires per hour. -- Feel free to correct me if my logic is faulty.

DrPcFix

Found this -- useful to determine buffer tank size:

Rich_49

I completely agree with the zoning strategy you describe . Room by room control is useful and when the budget allows is just fine . Differing temps , wind exposure , room load and use patterns all make it feasible .

There are still too many circs though . Just saw that you posted something about tank sizing when I was attaching the Taco presentation below . Just remember that your smallest load is not at design but at even higher temps . Smallest load is also a few of the smallest zones with similar exposure to conditions most times or else you'll end up with a 1,000 gallon buffer , LOL.
Take some time to figure out which zones will call together during winter usual wind direction at your location and then size the buffer to that load .

I suggest measuring the installed baseboard also and comparing it against room loads at design and higher temps to determine if there is an opportunity to use lower water temps and come up with a proper ODR curve for them .

Paul48

I completely understand the desire to have control over the heat in every room in the house. However, it would be nice to keep the boiler condensing, based on the heat load of the home, and not have to create a false load.

Rich_49

Condensing has to do with temp not load . Storage and buffers deal with keeping the equipment from short cycling . Another real nice thing is that buffers often times hold the boiler out . The only mod/con boiler more efficient than one that is condensing is one that is off .

Paul48

Really......how do you make a boiler condense with no load?

Rich_49

Paul ,
the load can be 100,000 BTUh . But if the temp is required to be 180* not much condensing is gonna happen . On the other hand if the required temp is 110* a whole lot of raining will happen in the HX .
Really , what kind of question is that ?

Paul48

Really.....Rich.....Did you not know what I was saying? Was your response to me, necessary? It left me saying to myself...what?

NYplumber

Take a look at the new Vitorossal 300 Cu3A by Viessmann. IMO let the boiler do its thing with its on board control. You have a nice high mass boiler with good control backed by a good company.

jonny88

Rich would this be a candidate for HTP with no need for a buffer tank.Also am I missing something but how are you going to purge each zone.Be nice if you got in there before it was all put together as I am sure there would be a lot of changes and I mean no offense to installer.Nice work and I know you put a lot of time and effort into it.Keep us informed as to how you proceed.

Rich_49

Jonny ,
This would be a great place for an HTP Pioneer (PHR-100 or 130 ) . The only circs that would be required are the ones for the zones also .