Net Seasonal System Efficiency

Mike T., Swampeast MO

In a converted gravity system it's hard for me to imagine constant circulation <I>without</I> TRVs.

The flow rates are too high and the delta-t too low. Variable-speed injection can really help but that relatively simple sounding concept is actually quite expensive and complex...

Mike T., Swampeast MO

This is in another post, but many won't see and would appreciate opinions.

Are these numbers in the realm of possibility? Fully TRVd standing iron system with outdoor reset and constant circulation. No changes to system besides boiler and curve adjustments. No form of primary/secondary with either boiler. Only temp "protection" for cast iron boiler was a differential pressure bypass adjusted for some bypass in all conditions.

Traditional cast iron (2x oversized based on I=B=R): 45%

Vitodens (operating at same curve as iron boiler): 88%

Vitodens (optimized curve): 97.5%

Brad White_9

Seems entirely reasonable, Mike,

The double-sized CI boiler number confirms what my Susan had to endure, spending $500 last month to heat an 1800 SF insulated home. Her radiation is capable of 67,000 BTUH at 170 F AWT. Her Burnham Series 2 (#206) with 164 MBH input has an output of 136 MBH. Damned close to double, eh?

The Vitodens with curve adjustment? You are doing God's Work. She told me.

Mike T., Swampeast MO

And the amazing thing (to me) is that this was a relatively modern cast iron boiler--only real difference between it and new is that it has a pilot light and no flue damper. Possibly no difference after a decade or so considering electronic ignition and flue dampers aren't the most reliable things in the world and are often eliminated.

The 2x oversizing (according to many here) is still quite common even with new replacements!

On these standing iron systems any condensing/modulating boiler should be able to achieve similar fuel reduction--even without the TRVs. I seriously doubt that even a properly sized and ideally installed/operated conventional boiler would be capable of nearly this degree of reduction--the required temps in the system are just too damned low!

EVERYONE should be using this technology on these systems! DO NOT OVERSIZE THE BOILER UNLESS SIGNIFICANT SYSTEM EXPANSION IS IMMINENT! Conduct a thorough heat loss and trust your numbers! Make certain that the homeowner understands both how to adjust the reset curve and that the lowest possible curve to meet the need will result in significant fuel savings.

CC.Rob

Apologies in advance for thread-hijack, but Brad, you are nearly describing my house. Built 1979 at 1800 SF, expanded to 2100 SF in 2005. Have about 64k BTU/h worth of baseboard, plus an indirect water heater (hence BTU question in another thread). The indirect would appear to have a demand about ~37k BTU/h at full load. Total peak demand would be 101k BTU/h.

I have the same Burnham 206 gas-fired unit. I've been getting educated and now backcalculating whether we are significantly overboilered, and what steps we might take to improve efficiency.

Am presently thinking a Tekmar 260. We live in a climate very similar to Brookhaven, where they did the recent tests on condensing/non and found resets help non-condensing as well. Comments? Thanks.

Brad White_9

Rob

no worries on the hijack; this is all a conversation. What have your heating bills been might I ask?

My Susan's house was built in 1928 and could be tighter but I see the similarities. Part of your issue is firing to limit to make domestic HW. Yes you meet the load but drive up a ramp to get there.

I suspect your indirect load is higher. What you cite is similar to a direct-fired unit. Indirects often have 2-3 times that input capability for a 40 gallon unit. Fast recovery is the name of the game, so it can get back to work heating the house. My Monitor MZ sends all it's capacity to the companion heater (which it gratefully receives). Tank is at temperature in ten minutes more or less from a cold start.

At least your total connected load is halfway of the difference heating to output. But you are also a candidate for a smaller boiler or a separate fired DWH heater.

Using a Tekmar 260 will take the guess work out of it and make it the best it can be. But remember if OD reset is your game and you fire the 206 every time DHW takes priority, you want to decouple the boiler and radiation loop to avoid spikes. There is enough water there to maybe cause that.
Your load disparity would justify decoupling the loops to avoid boiler condensation and to allow deeper re-set ala Brookhaven.

CC.Rob

thanks for the hijack dispensation. It is after all related to efficiency....

We use about 125 +/- 10 CCF per month to heat the house in the peak winter (Falmouth, MA). Based on summer usage, DHW is about 21 ccf/mo, and a gas stove is 2-4 ccf/mo. So winter total ccf is ~150 ccf/mo

Bought the house six years ago and have slowly been making it tighter, insulating, replacing some truly awful windows, etc. A real late-70s fixer-upper.

We basically have to live with the system; I want to try to increase efficiency without breaking the bank, and at first glance something like a Tekmar 260 would appear to fit the bill. It has a DHW priority so that would appear to address a concern above. The Burnham 206 is two years old. Not an option for us to replace at this point in our fiscal lives. If I only knew then what I know now about home heating, pumping away, etc.....

Not sure I follow you on decoupling and spiking. Can you elaborate? The system presently is set up with one circulator driving two heating zones and the indirect on a third zone. In order to do the Tekmar with DHW priority, as I understand it, we put the heating zones on their own circulator, and the DHW on its own. That what you mean?thanks.

Brad White_9

The spiking

is not so much a concern from what you describe, Ron, with the indirect on its own zone. But it still can affect you as your system is described. I will explain below.

(If it were a 3-way valve diverting to the indirect, it may have been more of an issue.)

Here is what I mean by "spiking":

Say it is 45 degrees out and you are running along at 120 degree water (not healthy in cast iron but bear with me here).

The DHW heater calls and fires the boiler to 180 degrees or to limit. During that time your heating zones will see that water for the duration. That is a spike, a burst of heat that is not controllable except by overheating the space and shutting down your circulators. It momentarily defeats your setback and affects comfort. Sudden expansion of baseboard, awareness of it...

Ideally when you de-couple the boiler from the cast iron boiler (4-way valve is preferred but there are several other ways too) you set up a situation of independence.

The radiation loop takes what hot water it needs from the boiler. When DHW calls, the 4-way radiation mixing valve responds to higher boiler temperatures and takes less of the hotter water to do the same work.

The loop temperature serving the radiators is thus unaffected by spikes in the boiler. Each side (indirect from boiler and heating loop on it's own valve) gets what it needs and the boiler is protected from too-cool return temperatures. Your setbacks can be deeper and that increases comfort and saves you money...

Yes, separate circulators for domestic and for heating although you can keep the heating side and control valves I assume you have now for local control. Having your own DWH circulator gives faster response I find, to meeting DHW demand.

Ron Schroeder

One thing to be carefull about in comparing condensing boilers to non-condensing boilers is to make sure both boilers are rated the same way. In the United States, 100% is when the output is equal to the total thermal energy of the fuel but in Europe (where most of the condensing boilers come from), 100% is when the output is equal to the NON-CONDENSING energy in the fuel. That is why some condensing boilers are spec'd at over 106% efficiency.

Mike T., Swampeast MO

Glad to have post "hijacked". In that regard though I'm stepping out on a limb a bit further than normal given my actual experience. Corrections greatly appreciated!

I've been getting educated and now backcalculating whether we are significantly overboilered, and what steps we might take to improve efficiency

64,000 btu/hr worth of baseboard "standard" 180° average temp rating? That works out to 30 btu/hr/sqft of output ability so your baseboard is likely somewhat oversized. To get an idea of how much oversizing of the baseboard you need a heat loss calculation. Have you done such?

Burnham 206 has a DOE capacity of 136 mbh and I=B=R of 94 mbh. Based on the output of the baseboard at 180° average your boiler would appear to be quite oversized--actually somewhere between "quite" and "extremely" based on your actual heat loss and level of thermal improvements...

The requirement of the indirect should NOT be added to the boiler's output rating over space heating! Doing so only reduces the space heating efficiency of ANY type of boiler. With an indirect of proper storage capacity based on the peak DHW demand and "reserve ability" of the boiler there [usually] won't be a problem unless your peak DHW demand occurs at the same time that you're trying to recover from space temperature setback. (BTW, such is ALWAYS a potential problem if the control system uses DHW priority.)

My gut feeling in your case is that the current boiler is quite oversized and your baseboard somewhat oversized. Reset can help--but don't expect miracles. For minimum cost while still protecting the boiler, I'm thinking a thermostatic bypass valve ESBE type TV to maintain 140° return and lowering the aquastat to the lowest possible setting to maintain comfort in the coldest weather. If your system is also typically overpumped, you'll likely be surprised at how little the aquastat needs to be set above 140°. Downfall here is that your DHW capacity might suffer. In such case you'd need a the simplest possible controller that allows for a different supply temp under a call for DHW.

Mike T., Swampeast MO

Quite aware of that. Am basing this on the American standard. If calculations are anywhere near accurate, I'd be well over 100% this year by the European standard...

Ron Schroeder

Hi Mike,

One of the reasons that I brought it up is that I have seen the two methods mixed in the same companies own literature.

Mike T., Swampeast MO

As have I, but honestly believe that most are an honest as opposed to intentional error. NASA managed to miss a Mars landing because one group assumed that another was using metric vs. US.

CC.Rob

Have not done full heat loss calc yet. It's on the list for the next couple weeks. Following another thread here to help me decide which program to use. Have played briefly with Hydronic Explorer, also hear good things about HVAC-Calc.

Yes, 65k worth of ~560 BTU/hr baseboard @ 180. If also accounting for loss in bare piping, then maybe we get to 68k.

Anyway, the house was built during a time around here when a lot of fly-by-nighters came in and threw up houses. This is definitely one of them. I know carpentry and man this place is a real piece of work. A combination of corner-cutting and incompetence pervades. Suffice it to say that the house was only slightly better insulated than a cardboard box. That's probably why oversized on the baseboard, but could also be incompetence. Place leaked like a sieve. We've added insulation, sealed, replaced crappy windows, etc. It's getting better.

Not sure how we ended up with a 206, but we did and it's not going anywhere. Not expecting a reset to work miracles, but given our climate I could see a 15% gain as realistic.

Brad, I think I'm getting what you're saying about how to plumb/valve for the reset. I'll have to draw it out this weekend. From what you're saying, it sounds like I can keep the single circulator with three zone valves, but need to valve everything properly with a 4-way rad mixing valve. What is the minimum return temp to keep the boiler healthy?

Mike T., Swampeast MO

What is the minimum return temp to keep the boiler healthy?

140° is widely regarded as the "magic" number. That's why I suggested the ESBE type TV valve. It will fully bypass the emitters until return temp reaches 140° then allows flow to the emitters while regulating bypass to maintain 140°.

soot_seeker_2

Minimum Return Temp

Are you talking strictly LP and NG or including oil in that figure?

Brad White_9

HWR temperatures

Generally speaking you want to keep your HWR temperature about 130 to 135 F minimum. Some say 140 to be safe and that is almost universal in some circles. 130-135 is pushing it, I admit. The dewpoint of flue gas varies with CO2 levels among other factors and can range from 127 to 136 F. There is a school of thought that says the HWR temperature has to be 5-10 degrees lower than that before condensation really starts. But why take chances?

Tekmar has a nice line of products including modulating valves, actuators, sensors. They also have some essays to assist your understanding. Given that you are keeping the Burnham use a 4-way. If you use a 3-way you will see raw HWR at whatever temperature.

Tip: If you had a condensing boiler, you definitely want a 3-way if you are mixing down. A 4-way will pass some HWS back to the boiler to defeat condensation.

Mike T., Swampeast MO

Believe it's different for fuel oil. Regular fuel oil is exceptionally uncommon for heating in my region. Only oil burners I've heard of use waste oil.

Ron Schroeder

Oil can take a lower return temperature. The actual minimum return temperature depends on not just the fuel type but the boiler design too but oil can go about 20 degrees cooler than NG.

With your way oversized boiler, it looks like you could benifit from a buffer tank to reduce short cycling losses and excess wear and tear on the boiler.

By the way, I personally prefer a seperate circ for the DHW indirect especially if the boiler temperatures are below 180 degrees. And don't skimp on the pipe size from the boiler to the indirect either to get rated recovery. The flow on my own system to the indirect is more than twice the flow needed for the 14 heating zones if they were all calling at the same time.

gasfolk

TRVs on Gravity Conversion

Mike,

Do you think the nature of gravity conversions (when well done by the Dead Men) make them well suited to constant circ *without* TRVs?

We are considering (but would like to avoid the expense of) TRVs on our gravity conversion.

gf

gasfolk

TRVs on Gravity Conversion

Mike,

Do you think the nature of gravity systems (when well done by the Dead Men) make them well suited to conversion to constant circ *without* TRVs?

We are considering (but would like to avoid the expense of) TRVs on our gravity conversion.

gf

gasfolk

TRVs on Gravity Conversion

Mike,

Do you think the nature of gravity systems (when well done by the Dead Men) make them well suited to conversion to constant circ *without* TRVs?

We are considering (but would like to avoid the expense of) TRVs on our gravity conversion. Are their new subtlties to your recommendations for when and where to use TRV?

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Mike,

Do you think the nature of gravity systems (when well done by the Dead Men) make them well suited to conversion to constant circ *without* TRVs?

We are considering (but would like to avoid the expense of) adding TRVs on our converted gravity system when we replace the boiler. Are their new details to your recommendations for when and where to use TRV?

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Do you think the nature of gravity systems (when well done by the Dead Men) make them well suited to conversion to constant circ *without* TRVs?

We are considering (but would like to avoid the expense of) adding TRVs on our converted gravity system when we replace the boiler. Are their new details to your recommendations for when and where to use TRV?

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Do you think the nature of well designed gravity systems make them well suited to conversion to constant circ *without* TRVs? Are their new details to your recommendations for when and where to use TRV?

We are considering, but would like to avoid the expense of, adding TRVs to our converted gravity system when we replace the boiler.

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Do you think the nature of gravity systems make their conversion well suited to constant circ *without* TRVs? Are there new details to your recommendations for when and where to use TRV?

For our boiler retrofit, we are considering but would like to avoid the expense of adding TRVs to our converted gravity system.

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Do you think gravity systems are well suited to conversion to constant circ *without* TRVs? Are there new details to your recommendations for when and where to use TRV?

For our boiler retrofit, we are considering but would like to avoid the expense of adding TRVs to our converted gravity system.

Thanks,

gf

gasfolk

TRVs on Gravity Conversion

Do you think gravity systems are well suited to conversion to constant circ *without* TRVs? Are there new details to your recommendations for when and where to use TRVs?

For our boiler retrofit, we are considering but would like to avoid the expense of adding TRVs to our converted gravity system.

Thanks,

gf

PJO_5

Other Factor?

Mike,

I've been following your "tweaking" and this is great stuff...

Did you say at one point that the average air temp. (t-stats used to run the old system I assume) in your house is reduced significantly now as compared to before (w/ old boiler)? What was the usual temps with the old system vs. new?

I assume it's all relative to comfort, and because your are still comfortable (more comfortable probably) at lower air temps that is a big reason. The MRT is what really is going on I suppose, right?

Thanks, PJO

Mike T., Swampeast MO

This year I'm in "Eurocave mode". Space under renovation and lightly occupied rooms average about 55°F. Occupied space about 61°F. Am using a forced air electric boost most workdays--one time up to about 66°. Two of the baths with radiant floors are hovering around 58°--they honestly feel warmer than that temp would imply and aren't too bad to use. Mild winter. Comfort has definitely dropped this year but not bad with a sweater and cozy comforter.

Last year (1st for Vitodens) renovation space about 60°F and occupied about 66°F. No electric boost. Normal winter.

Year before that (last for conventional boiler) indoor conditions similar to this year with most occupied space about 64° and occasional electric boost. Mild winter.

Year before that indoor temps more similar to 1st year with Vitodens. Slighly cold winter.

Previous attempts at such low temps with the conventional boiler were mainly futile. Comfort dropped much faster than fuel consumption. With the Vitodens, fuel consumption has dropped much faster than comfort.

Did adjust heating load based on the different indoor temps. The 9½% increase in efficiency this year is mainly the product of lower system operating temperatures. Until the outside temp drops near freezing the average operating temp across the boiler is about 69°F with extremely low delta-t.

Maximum supply temp this year was 124.9°F @ 4.9°F outside. Maximum return temp this year was 99.1° during the same cold spell.

Mike T., Swampeast MO

January utility statement just arrived and predicted use agreed with actual use to the therm. 60 therms and 200 kwh for space heating 3,600 sq.ft. 1903 home in January--not too bad. Granted warm January and cool house, but easily $200 in fuel savings in just this one month compared to the old cast iron energy waster. If natural gas doesn't come down in price (not looking as likely as a couple months ago), Mr. Vito will pay for himself very rapidly.

S Ebels

\"If natural gas doesn't come down in price \"

I think we're at the new average "bottom" for fuel prices. We'd better get used to it. The Arabs have figured out they can charge these prices for fuel and the world isn't coming to an end. It's here to stay.

adayton_2

!!! HIJACK !!! Mike

:-). I see you guys knowledge and this thread re: 4way mixer, come close to my needs. I posted about a special Taco 3 way (http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=34701&mc=1) but the post ended up halfway down the page in 1 day with no responce. (one would think its the busy season lol :-) )...Please check out this post Re: Taco 3 way mixer CASCADING.....I need help in cascading a Taco following another mixer. Thanks

Al/Jim