Feedback on boiler replacement

Dave_KC

In the design stage with plumber on replacing our 18 year old Munchkin 199M and would be grateful for some feedback on the design, prior to beginning installation.
Some background:
* Feeds DHW loop (plate HEX) and CH loop (fan coils).
* The DHW loop requires a higher temperature than the CH loop - especially when the outdoor reset lowers the CH setpoint.
* The 199M is overkill for our CH needs, but works very well for the DHW.
* In cooling mode, the CH loop is fed by chillers and provides AC, but 199M still supports DHW


Some questions -
1) Are the zone valves necessary on the outlet of the boiler? The thinking is if 1 boiler is supplying DHW, and the CH primary loop pump is running, the outputs may feed the CH side without the valves (and vice versa).
2) I see quite a few installs using Alphas/smart boiler pumps. I'm confused to the benefit of these in the secondary loop, since they are only used when the boiler is firing and it cannot modulate the pump.
3) My guess is that a DirtMag or equivalent would be beneficial, however with 2 inputs to the boiler, where is the best placement for a separator?
4) Where does one install drains to make boiler maintenance/flushing easier?

Thanks everyone!

mattmia2

I have some ideas but what are your DH emitters? Is it only fancoils or are there other emitters in there too?

What is the HX for? Isn't that just an indirect with a coil in it?

Dave_KC

Just the fancoils, each with their own thermostat.
Very similar to an indirect, but it's a buffer tank with external plate heat exchanger, so it stores no potable water.

GGross

Yeah I need to know what the plan is for the plate exchanger, not sure what it could be doing piped in the location shown

Dave_KC

The two primary loops are already in place today with the Munchkin and work very well. Here's a picture of the HEX used for DHW. Our setup is very similar:

mattmia2

You can make this a lot simpler.

The UFT100 is discontinued.
If you use an EFT series you get a 10:0 turndown ratio and get about the same low fire rate as the cascaded UFTs.

You should use an indirect instead of the buffer tank and HX. I will cost less and will be less prone to fowling on the DHW side.

Unless your DHW demand is nearly constant, you should size the boiler for the DH loads and make the indirect large enough to cover your DHW demand with that boiler size. This will let the turndown of the boiler better match the DH load.

You can use the DHW control on the boiler to fire the boiler to the DHW setpoint and the DH control to control the water temp for the DH load using the outdoor sensor and reset curve. You can either set up DHW priority or allow the water at the DH setpoint to go to the fancoils because the higher temp water won't hurt them. The fancoils will need fairly hot water anyhow, most of the benefits of the modcon will be lost using fancoils.

The only benefit to cascaded boilers here is redundancy but it will cost a whole lot more for that redundancy.

mattmia2

The UFT series is discontinued.

1 EFT can get the same turndown as cascaded UFTs because the UFT is 5:1 turndown and the EFT is 10:1.

Unless you have a nearly continuous DHW load you should size the boiler to the DH load and make the indirect large enough to store enough water to cover the DHW load. The indirect will foul a lot less than the HX and will simplify the system.

The DHW can call the boiler on the DHW terminals and the fancoils can call on the DH terminals and have a reset curve set in the boiler. The faincoisl will need fairly hot water so the mod con will not have a whole lot of benefit. The fancoils can tolerate the DHW temp water so you don't need to limit the temp for them.

You don't need the buffer tanks unless the one in the DH loop is needed for the cooling. The turndown of the boiler is enough to more or less match your fancoils(unless there are many small fancoils) Should have a flow check on the injection from the boiler in to the DHJ loop and from the chiller in to the DH loop(unless the cooling is just a HX right in the DH loop).

You can make this a lot simpler than what you have.

Hot_water_fan

I don't understand the zone valves either - their manuals never include them and if the boiler pumps have flow checks, they seem to serve no purpose.

What is the CH Buffer tank? It could serve as your separation and if a 2-pipe buffer, provide the buffer + rapid response.

Dave_KC

Thanks for the response:
@mattmia2 -
HTP is telling me the turndown ratio is 10:1, https://htproducts.com/literature/mktlit-81.pdf Unless they're fibbing. I understand your recommendation for the indirect. The Plate HEX requires 160+ degrees to function correctly, but gives endless DHW. Sounds like the indirect would require fewer btus over a longer period of time, but I would have to pony up $$ for a new indirect. The Plate HEX works very well with the 199M, but it does require cleaning annually.
There are many small fancoils (15), however I think the buffer tank's original purpose was to prevent the Munchkin from cycling. But since the UFT's turndown ratio is much lower, might have to rethink this. Valid point that you make.
Currently, the fancoils run off Vision 1's curve. They are double row and seem to do well regardless of the incoming temperature. Forgot to mention, the primary loop for the fancoils is over 200', so if the loop is allowed to cool, it takes awhile to bring back up to temp. Hence why the pump continuously runs on the loop.

@Hot_water_fan -
HTP does not recommend the zone valves, but the plumber did. HTP does not have the CH pump running continuously, as we do, but only when there is a call for Central Heat. I've seen it in our current 199M system where DHW calls for heat, and it also feeds heat into the CH loop. Plumber said it was thermosiphoning as it only happens on rare occassions. And it's piped exactly how HTP specified.
The CH (Central Heat) buffer tank is to maintain some btu mass so the boiler doesn't come on each time a fan coil comes one.

Any comments on the other questions in the original post?

mattmia2

You could put a dirtmag in it, but you have very limited ferrous components and a closed system. they are mandatory on a system with cast iron emitters, but it isn't super important here.

The man place you need valving is to clean the dhw side of the hx, the rest would only be if you need to repair something.

EVM circulators use a lot less power than conventional motors and are more adjustable.

A uft is 5:1 but also discontinued. The new fire tube HTP boilers are 10:1.

hot_rod

Some unusual piping

Why a pressure bypass valve in the loop?

Piped in and out I don’t see the buffer doing much?

ECM save 50% or more electricity. I would use a mag sep with any system that has ECM circs

An ECM with zone valve works very well.

I like the plate HX option, price an 80 indirect and see why😉

Check out how Energy Kinetics maximizes an external plate dhw hx

If the HX was piped as a parallel load you could run much lower boiler. If it us sized large enough you could develop DHW with maybe 150 SWT, maybe run some condensing mode. A 199 should get you a constant 4 gpm or more.

Most indirect tanks don’t have enough HX for continuous DHW, so you need the tanks dump capacity. So if you like endless DHW, keep the plate HX option.

A 4 in 1 hydro sep could clean all that up and give you excellent air, dirt, mag and hydraulic separation 

Screenshot 2023-05-02 at 8.57.50 PM.png

Dave_KC

Thank you for your input, Bob. To address your questions:
* The bypass valve was suggested by both HTP and the Chiller manufacturers. My guess is that since we're using a fixed speed pump, and with all the fan coils turning on and off, the bypass valve is to provide the boiler / chillers a steady return flow rate. 18 years ago, we didn't have many variable speed pumps to choose from.
* Seems to be a consensus to remove the buffer tank. My only concern would be if removed, would it cause the boiler to fire more often, and short cycle? I would guess there is 8 gallons of water in the loop without the buffer tank, not including the amount in the boiler.
* I really like the HX setup presently. No concerns about running out of hot water, but it does require a large amount of BTUs to keep it going. The munchkin 199M will run constantly at full throttle when a bath tub and shower are running simultaneously, but only a few minutes afterwards to replenish the 30 gallon buffer tank.
* On the ECM pumps, I'm trying to justify their extra expense for the boilers. On a main (primary loop) running constantly, I can see how their up/down modulation can save some energy based upon demand, but when feeding a boiler only when firing not sure there's much savings there. Plus another electronic device to have issues with.

mattmia2

An ecm circulator uses less power. The motor is more efficient. the cost of the circulators is negligible in the grand scheme of the project.

I don't know enough about how the cooling works, it may need the buffer tank.

Dave_KC

I understand now on the ecm's, thank you.
The chillers have a separate, well insulated tank not in the pictorial above. If I can get rid of the 50 gallon heat buffer tank without causing boiler issues, the design could move to what I think you've been mentioning above. Sounds very similar to what HTP lists in their cascade design.

mattmia2

What are the capacities of the fancoils? A single EFTU-199 will turn down to about 20,000 btu/hr so if the smallest of your coils are about that size or larger a single boiler and no buffer tank will modulate down to that(assuming you don't lower the swt that much).

If you reduce the supply temp to the fancoils much you need to reduce the blower speed or it will feel cold and drafty, if they can't do that you will be limited by how low your odr curve can go.

hot_rod

As for DHW, it takes X amount of btus to heat water regardless of the method, tankless, combi, separate HX, fired or indirect tank.

I feel the most $$ efficient way is with a mod con, and generously sized HX.
No standby loss, near constant hot water. It just depends on how you use of want your DHW supplied.

An indirect with a large amount of HX would come close. Dual coil indirects give you a lot of surface area, and can tun lower boiler temperatures, fast recovery, etc.
Or a reverse indirect with the triple copper coils.

If a dump load and a 30 minute wait for recovery is acceptable a smaller boiler input could be used with an 80 or 120 indirect.

It a purely heat exchange and BTU input game, regardless of how you cut it. There is no one right answer to DHW production.

Mixing hydronic heat with chilled water in a two pipe system does add some challenges. The chilled side probably runs a tighter deltas, so more flow requirement.

Was a heat and cooling load calculation every done? That is always the best first step for sizing everything, boilers, chillers, pipe, pumps...

Dave_KC

The fan coils heating capacities range from 20,000-48,000 btu/hr. They have low/med/high speeds, but are generally set to medium for heat and high for cooling via the thermostats.
When the house was built 18 years ago, the load calculations were performed to initially size everything. We had new chillers & fan coils put in 2 years ago, and they revisited the cooling load then. And you're correct, the pump on the chillers are substantially larger, but surprisingly have small heat exchangers.
Still on the fence for the DHW, for now I think we'll keep the current plate HX. We've had it for a couple of years and no real complaints.

mattmia2

if the dhw is already there and can be reused without a lot of reworking of the piping it could be more cost effective to go with the bigger boiler. If a single smallest fancoil is calling it could short cycle without the buffer tank if there is much of a reset curve. I'm not sure that odr gives you a lot of advantage with the fancoils because their output really falls off when you get in to the temps that would make the boiler condense. you would almost have to rework the fancoils with much larger coils and blowers that modulated on air or water temp to make odr make a big difference.

Dave_KC

It is certainly possible one small fan coil is calling for heat, but normally a few of them are running simultaneously - especially when cold out. Just replaced the fancoils, so wouldn't want to tackle that again anytime soon.
The heat buffer tank is 18 years old, so it's days are probably numbered. Are you suggesting leaving it, maybe use a smaller one - to offset boiler short cycling?

hot_rod

The smallest load is 20,000? A 199,000 turns down to 19,000.

Or maybe two 110,000 That give you a 20- 1 turndown with a 12,000 low end.

Price and features it's hard to beat the Lochinvar Knights. Many other good brands out there.

The buffer may be more for the chillers?

mattmia2

hot_rod said:

The smallest load is 20,000? A 199,000 turns down to 19,000.

He wants to do ORD on the fancoils. I'm not sure that will work out anyhow. I suppose he could use some of the anti short cycle features on the boiler if a single 20,000 btu zone is calling alone on odr for long enough to cause short cycling. That is probably the better option than the buffer or cascaded boilers, it is likely if a single fancoil is calling for an extended period it is going to be when it is pretty warm out so as long as the blower is controlled on an aquastat the boiler holding off firing to reduce short cycling won't be noticed.

hot_rod said:

The buffer may be more for the chillers?

We covered that, there is a separate buffer thank for the chiller.

hot_rod said:

Or maybe two 110,000 That give you a 20- 1 turndown with a 12,000 low end.

That probably makes it more complicated and expensive than necessary although it does give redundancy.

Dave_KC said:

The heat buffer tank is 18 years old, so it's days are probably numbered. Are you suggesting leaving it, maybe use a smaller one - to offset boiler short cycling?

The buffer tank isn't like a DHW water heater where it is constantly exposed to fresh water with fresh oxygen and minerals, it likely will last many decades.

Dave_KC

Thanks again for your feedback. Much rather be having these discussions now, than after things are installed!
Would you mind expanding on this statement, I don't totally understand. "as long as the blower is controlled on an aquastat the boiler holding off firing to reduce short cycling won't be noticed."

Dave_KC

On a side note, I pulled up my natural gas usage from the past few years. During the winter months, the usage is from 150 - 360 CCF per month. On the highest month, my rough math equates this to about 1,200,000 btus/day. Of course this is only an average, we don't receive daily readings, only monthly.

And after having waiting on parts for the Munchkin for several days in the middle of the winter, I'm going with redundancy.

mattmia2

Dave_KC said:

Thanks again for your feedback. Much rather be having these discussions now, than after things are installed!
Would you mind expanding on this statement, I don't totally understand. "as long as the blower is controlled on an aquastat the boiler holding off firing to reduce short cycling won't be noticed."

If the anti short cycling holds off the boiler from firing on a timer or until the water temp falls to a certain value, if the water temp falls too much and the blower is still running then it could feel drafty as the air gets cooler. If the blower is controlled on an aquastat that senses the water temp at the coil then the blower will shut down, if the blower is just controlled by turning on with some delay after the call for heat starts then if the boiler shuts off on high limit then stays off for 5 or 10 minutes on the anti short cycle timer and the water temp falls significantly the blower will continue to run until the thermostat is satisfied(may also have a delay that runs it for a fixed period after the thermostat is satisfied to get more heat out of the hx).

You need to check the manuals to make sure they can cascade different size boilers, but if you cascade say a 150,000 btu and 50,000 btu both with a 10:1 trundown then you can get around 5000 btu/hr minimum firing rate. You probably would want to fire the smaller boiler before the bigger boiler.

Hot_water_fan

On a side note, I pulled up my natural gas usage from the past few years. During the winter months, the usage is from 150 - 360 CCF per month. On the highest month, my rough math equates this to about 1,200,000 btus/day. Of course this is only an average, we don't receive daily readings, only monthly.

KC is Kansas City? That's a heat loss of under 100,000 btu if your highest usage was 360 CCF during a month of ~1000 HDD 65. I'd like the 2x 80kbtu setup.

tim smith

Using the plate style heat x, you probably cant get more than 4 gpm at 120 out of it with btu available as long as heat x sized right. Thats fine for a couple semi conservative shower heads but not for an 8-10 gpm tub fill. This would be my main concern on using the flow through option vs some potable hw storage.

Dave_KC

Plumber had a thought on the fan coils causing the boiler to cycle. Use a small, well insulated, electric water heater for the buffer tank. Then the water heater would suffice the demand for the occasional fan coil request. And when increased demand occurs, the boiler(s) takes over. Basically, the electric water heater becomes the smallest heat generator in the system to prevent the boilers from kicking on.
And the fan coils and thermostat are dumb. Turns on when below thermostat setpoint, turns off when above setpoint.

Hot_water_fan

An electric water heater with or without the elements? I wouldn’t want to use resistance electric to heat the house. 

Buffer tanks are easy tech, pipe it correctly and you can roll. 

hot_rod

Any time you are below a design condition the boiler will cycle. Even with the boiler output matching the fan coil exactly.
Now on a design day a 20 k fan coil should keep a boiler turned down to 20 k running continuously

Most agree a 20 minute or more run time is best practice.

The math to size a buffer for a mod con is fairly simple once you identify the smallest load, and the desired run time. Download Idronics 17 for buffer ideas

hot_rod

Here is an example of a 1,500 btu load on a boiler that can modulate down to 10,000.
Looking for a 20 minute run time, 20 degree delta in the tank. Plug in your own numbers.

Dave_KC

I've been reading Caleffi's idronics journal about thermal storage. It presents some options that seem to simplify the install, as well as reduce the number of components needed. It appears the buffer tank takes place of the hydraulic separator, and can be shared as both the heating system buffer thank, as well as the DHW thermal storage:




Questions:
1) If the indirect with internal tank only has 1 1/4" inlet & outlet, will this satisfy the short / fat headers needed to minimize head loss?
2) In times when there is a call for both Central Heat & DHW simultaneously, it appears these approaches prioritize Central Heat? Could one switch the zones, so DHW would be the priority?

hot_rod

The upper drawing is direct to load piping, a 2 pipe buffer.
One downside is you would need to maintain that tank hot all the time fort DHW loads to satisfy quickly.
How hot depends on the tank and your expected DHW load. In some cases you may be able to maintain the tank at 140 or 160 for DHW. It comes down to the number of coils in the reverse indirect. ThermoMax has a great program for calculating all that. Contact a rep or the manufacturer directly.

Same for the second concept, you need the tank always hot.

What about the plate HX like one of these. The electric boost eliminates the boiler ramp up lag. The buffer temperature could be maintained via ODR, since the DHW is a priority load.

Dave_KC

Thank you, Bob. Yes, the tank would always have to be at DHW temperature year round.

In your examples, since the buffer tank temperature is controlled by the ODR, I believe the system temp sensor would sit in the buffer tank. Where would the DHW aquastat/sensor be placed in this arraignment?

hot_rod

Correct, boiler sensor or system sensor if you boilers have that option, go in the tank.

The DHW could be controlled by the boilers DHW function, on priority. When DHW flows, activated by a floe switch in the cold supply piping, the boiler fires, targets 180F.

Either the boiler reached 180 and shuts down, or the DHW call ends and the boiler shuts down. A thermostatic mixing valve prevents the DHW from getting excessively hot.

The heat exchanger gets sized by the flow rate you desire. With 180 boiler supply a fairly small plate HX can supply 4 gpm or more. Notice the size of the plate heat exchangers in combi boilers 3X8, maybe 6- 8 plates.

If you have a larger HX, then the boiler would not need to run up to 180F, keeping efficiencies better.

I've found a 5X12, 8 or 10 plate can generate good DHW with boilers running 140 or so.

The plate HX manufacturers sizing programs will dial in the HX size, exactly.

The sizing math is included in this Idronics.