why use primary/secondary if not needed?

Nom_Deplume

We're getting an HTP Elite FT boiler (110 KBTU/H)  installed in a few days. This boiler has the vertical fire-tube HX with larger water passages. HTP says P/S piping isn't needed if there is sufficient flow. There is certainly sufficient flow (house has old gravity system with monster pipes).



But installer is (not unreasonably) refuting me by pointing to the piping diagrams in the manual...ALL diagrams relevant to our boiler size show P/S piping. It's only in the promotional material that HTP says P/S piping isn't needed...pretty sneaky



Isn't it bad practice to use a energy-inefficient setup (one extra pump) when it isn't needed?



P/S is certainly the CYA setup, and it already exists from the previous boiler so it's also the "quick change artist" option. I realize P/S doesn't hurt anything...well, except the environment and my wallet, slightly.



Comments/advice appreciated.

pecmsg

Green?

Your worried about being green with an extra circulator yet you’ll keep the

“house has old gravity system with monster pipes”

 

Do what the installer want’s.

Nom_Deplume

say what?

What on earth are you talking about? Oversized piping and oversized radiators are wonderful and have no negatives for the environment.



but what about my question re. P/S piping? 

pecmsg

Sir

What about all the extra water that’s in the system? That’s going to cost extra $ to heat to temperature. Thats extra fuel burned.

Larger Pipes = more surface area. More surface area = more heat loss = more fuel burned.

 

But to answer your question, If the install manual recommends P/S piping then do it.

Gordy

Flow rates

If the system side can meet the minimum flow rates the boiler needs to maintain the proper delta t through the HX then no you don't need to P/S pipe it. But some math is involved to determine that. With the fire tube HX design that has less of a pressure drop it makes it more feasible to plumb the boiler direct, but you need to determine if the system flow rates are what the boilers HX needs to stay happy.



Generally P/S piped is the safest bet that the boiler will always get the proper flow rate through the HX at all times that's why it's recommended.





Gravity systems extra mass, and volume make for a wonderful built in buffer tank. It would be a shame to rip out perfectly good piping to reinstall smaller piping. That's not green either.

JStar

P/S

We install firetube boilers without P/S on gravity systems all of the time. As noted, make sure the flow rates will work. The extra water in the old system will nearly guarrantee that the boiler is running at super high efficienies all winter long. We typically see these types of systems at around 99% efficiency. Yes, the water takes longer to heat up, but it will stay hotter for longer and reduce cycle times by a significant margin. Installing P/S will make the boiler too hot too fast and cause short cycling, which will reduce the boiler life and destroy combustion efficiency.



If you want a solid answer, call the manufacturer yourself. First, measure the furthest piping run in the system and number of fittings. We can help you figure out the friction loss and flow rates needed.

Zman

primary/secondary?

Why would you with a gravity conversion?

I agree that the best path is to contact the manufacture. Don't argue with the contractor.

Carl

Nom_Deplume

thanks!

Many thanks for everyone's comments! (Except the advice to rip out gravity pipes---maybe I should rip out the floors and walls as well, that'll also reduce the thermal mass of the house!)  I will call the manufacturer.

SWEI

HTP Elite FT boiler (110 KBTU/H)

Did anyone perform a a heat loss calculation on the house?  If the answer is no, DO NOT PROCEED (you probably need a smaller boiler.)



You should be able to direct pump the boiler and size for a 30ºF ∆T on those rads.

Nom_Deplume

heat calc leads to too-large boilers

As I've said previously in another post, heat calcs lead to too-large boilers.



We've been using a XX KBTU boiler for years (I sized it using actual gas consumption of the previous boiler vs degree-days and doing a straightline extrapolation to a design day). It's been fine. But the contractor tells me XX KBTU won't heat our house, I need YY BTU. Why not? Because his calc says so.



It's basically "Who do you believe, me or your lying eyes?"



I realize few people will do what I did, but it can be done. All you need is look at old gas bills...actual usage, not theoretical calculations.

Rich_49

Be sure

you did not extrapolate and log that information during mild winters or you may end up with XX BTUs in a YY BTU winter .   A little more research and thought quite possibly would have led you or your contractor to the HTP Pioneer that certainly does not require P/S piping . You may also want to use a Taco Bumble Bee on the emitter side of what you are now purchasing , with that big pipe and low hydraulic pressure Rads you should be able to get what you need . Tell your contractor to do the math to determine if all will work .  If you are not comfortable with the contractor and his ability to provide you the knowledge , talent and integrity to install this new equipment , get another one .

Gordy

I agree with Rich

If you are going by gas bills that are estimated every other month it can skew calcs. Along with other gas appliances not being properly deducted if used, and using the btu input, or output of the boiler.



The best that can be done is using an hour meter on the gas valve of the boiler, and calculate run times, and degree days from that., or some thermostats have heat call time in a 24 hr period not as accurate.

nicholas bonham-carter

"Neither energy, nor matter can be created or destroyed

It doesn't matter how much water is being heated up, as long as it is not being thrown away. The amount of fuel burned will be determined by the heat-loss of the building.--NBC

Nom_Deplume

extrapolation

"Extrapolation" means you take the gas usage (actual, not estimated) in ANY winter (mild or not) and use that to CALCULATE what will be needed on a design day (since BTUs used are roughly proportional to the degree-days).



The Taco Bumble Bee is an interesting device, I didn't know about it. I have to think about how well it works when there is outdoor reset. If the water is 90F, as it is for my system in October or April, running the pump at dT=20 means the pump is not really running at all.

RobG

Another thing

Are there any other gas appliances in the home?

Nom_Deplume

sure

Sure, but summer gas usage gives you a baseline to subtract.



It's not as if this needs to be precisely accurate; you want the boiler to be slightly oversized, but not as much as heat calcs oversize it.

NYplumber

Bewildered

"Isn't it bad practice to use a energy-inefficient setup (one extra pump) when it isn't needed?"



It always bewilders me how people will penny pinch on minuscule details. The pump (assuming 007 or the like) in a residential application is not much more of an electric draw then the lights left on in the yard every night, or other power robbing electronics left plugged in.



Ask yourself, do you unplug the cable box, cell phone charger, computer, printer, etc when not in use? If the answer is no, then add the pump. If the answer is yes, call the manufacture to see if you can get away with it.

Gordy

Technically

If your heat loss, and boiler are a good marriage. The boiler should run at 100% during a design day scenario. So if your design day is -10 for a 24 hour period, the boiler will run flat out for that period. Highly unlikely that would happen, and design days occur on average 1% of the heating season. Speaking of a modulating condensing boiler here.



If it gets below a design day temp which does happen put on a sweater, and grab a blanket. That's getting the most energy efficient boiler size match possible. If you want to over size then pay the gas company.

SWEI

XX and YY

What size boiler have you been using for years?  What size is the installer telling you you need?  How many square feet is the house, and when was it built?  Have there been any envelope upgrades since it was built?

Rich_49

I am Aware

of the definition of Extrapolation . Many of my home performance friends like to extrapolate all kinds of things while MODELING homes that live in the software on their computer  I unfortunately have the task of keeping REAL people in Real houses during Real winters (possibly harsher than what you extrapolated for ) comfortable in their houses . I cannot tell you how many times I have heard from these well intentioned nerds that it worked in the model .  Funny thing about the systems we are talking about is the fact that in a harsh winter their efficiencies vary from not so cold times . No extrapolation is best left to scientists and guys in offices . When most of us design and install systems we want the customers to be warm on every day no matter what the outdoor conditions and second we , well I don't wanna be bothered with people that need toi where a sweater like a European telling me I did not do good enough .

Delta T varies on the amount of heat actually being emitted through the system . Supply water temp has nothing to do with Delta T . If the SWT is 90 and the Delta T is 20* and you are pumping 2.9 GPM the space used 29,000 BTU and if the temp stayed the same and you pumped 5.6 GPM the space received 56,000 BTU . I would hardly call that hardly pumping and in fact would call it efficient pumping and only using what you need and xconserving energy . So in April and October I guess using only 9/22/32/42 watts to give you what you need damn near to the enth degree really sucks huh ? 

Eastman

I feel like it's the other way around

Primary/secondary gets used as a penny pinching shortcut.  It's an easy way to avoid additional time devoted to analysis.  And a pump on a correctly sized modulating system will be running much much more than one on a conventional setup.

gennady

pump

are you saying the pump in this set up is controlled by thermostat?

Eastman

I'm not sure what your asking

By "conventional" I was referring to an on/off boiler incapable of modulation.



I mean, everything is ultimately controlled by some kind of temperature sensor.

Gordy

Not sure about your statement Eastman

Are you referring to the installer, or the RD of the boiler manufacturer ?

gennady

cost of pumping

Sorry, i was unclear. Primary secondary piping cost of pumping is lower then the one of conventional setup even with 1 extra pump running. Just my 2 cents.

Nom_Deplume

of course

Primary pump runs when boiler runs, and boiler runs when thermostat calls for heat.



In system with outdoor reset, the boiler runs most of the time, and so the extra pump in a P/S system runs most of the time too.

Eastman

well...

I think it's more about communication than research and development.  The manual should document the requirements involved for directly pumping their equipment.  The installer needs to spend the time to see if such a configuration is worthwhile and said requirements can be met.

Gordy

Hence

The math, and understanding of the appliance.