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Gordy

Calculating losses through usage is not as accurate as one may think. Boiler efficiency plummets on mild days.

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Gordy

Hatterasguy said:

Gordy said:

Calculating losses through usage is not as accurate as one may think. Boiler efficiency plummets on mild days.

That would be a fixed output boiler that is oversized for the radiation and a system without mass.

If any of the above changes, the efficiency is not severely affected.

Fundamentally, if you can get the boiler to run for 15 minutes, you're all set.

The problem is most pronounced on oil fired equipment feeding fin tube baseboard in houses less than 2500 square feet. Here is where the efficiency plummets markedly.

Fundamentally most existing boilers are drastically over sized no?

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Gordy

You can avg. a month 3 months what ever. Where the tire meets the pavement is design day, and even below with some knots blowing. If you don't have the right numbers the phone will be ringing.

With the release of higher TDR boilers it becomes less critical to oversize other than the cost of more boiler than needed. However having the extra hp to unleash when times go below design, and having the low end for small zones, and mild days is a dream come true.

Gordy

For example the Lochinvar KHN the 55's low end is 8k with a 7:1 tdr. the 85's low end is 8250 with a 10:1 tdr. If I'm on the edge with no allowance for below design conditions it won't kill the efficiency to bump up to the 85.

With the HTP uft things are a bit different because of the slot sizes they chose to implement.The 80 goes down to 8k next size up the 110 goes down to 11k so big difference. Both are 10:1 tdr.

I think loch did their slot sizes right to cover small load homes, and the medium load achieving near same low end for small zones.

Gordy

Depends on the load the 55 gets lashed up to. Depends on DHW needs. Why a fool?

Chester

If I had to do it over again I'd go with the KHN. My Greenstar 57 modulates down to 12,900 (input). 8,000 would be sweet.

SWEI

Hatterasguy said:

You are referring to the term "base temperature". It varies depending on the household

Base temperature is a term from the degree-day calculation. Many of us use the term balance point to refer to the outdoor temp below which a building requires heating.

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Mark Eatherton

Chester said:

"... doesn't break it down to an hourly accurate picture. Due diligence requires us to perform an actual load calc."

ME: Just curious why you need hourly. And I'd argue that historic is an actual load calc, just a different way of doing it.

I can see that if you're designing a new system you need much more granularity -- room by room, etc. But if you're just going to drop in a new boiler I'd think all you need out of a heat loss calc is to make sure that a) you can heat the place at design conditions AND b) you can fire low enough to manage off-peak loads for your smallest zone.

Glad you think it's a good conversation. Let's take it over to a fresh thread...and have a contest!

Because simply stated, boiler ratings are in BTU/Hour.

And other than that, your methodology does take a LOT into consideration, but it is only applicable to THAT application. Things that can and do significantly affect demand are solar gains, internal gains (how are you going to back out the wattage used internally, most of which ends up being heat?) human occupancy, etc. etc.

It's a good start, and done right can be dead nuts on, but a LOT of loose variables to account for. I prefer a gas meter, when available. At design condition,at the beginning of the hour, go to the gas meter and clock the boiler until it stops running. You can then extrapolate this information to determine "real time" energy consumption. And it doesn't have to account for solar gains, internal gains,etc.

ME

ben01

Wow, miss a little, miss a lot!

In my particular case, I'm not too sure I'd want to try and drop down to a lower BTU boiler. Other than initial savings on the actual unit, there wouldn't be a reason to do it correct? I would still be able to modulate down to hopefully achieve max efficiency, right?

as stated, by Hot Rod, all the threads regarding systems not keeping up have me more than concerned!

As far as system designers, any recommendations?

Thanks for all the help and replies!

Ben

Gordy

Depends on the boiler choice, zoning, and water temps. Cycling beats efficiency in the dirt, and zoning with out the low end capability does the same. Keeping your return water temps sub 130 will get efficiency climbing.

hot_rod

ben01 said:

Wow, miss a little, miss a lot!

In my particular case, I'm not too sure I'd want to try and drop down to a lower BTU boiler. Other than initial savings on the actual unit, there wouldn't be a reason to do it correct? I would still be able to modulate down to hopefully achieve max efficiency, right?

as stated, by Hot Rod, all the threads regarding systems not keeping up have me more than concerned!

As far as system designers, any recommendations?

Thanks for all the help and replies!

Ben

ben01 said:

Wow, miss a little, miss a lot!

In my particular case, I'm not too sure I'd want to try and drop down to a lower BTU boiler. Other than initial savings on the actual unit, there wouldn't be a reason to do it correct? I would still be able to modulate down to hopefully achieve max efficiency, right?

as stated, by Hot Rod, all the threads regarding systems not keeping up have me more than concerned!

As far as system designers, any recommendations?

Thanks for all the help and replies!

Ben

Some thoughts about finding a designer.

A heating system is a large investment, like a new truck, but it cannot be returned if you are unhappy, like a truck

I'd interview a hydronic designer like you would a doc or attorney. Hydronics it is a specialized trade, so find an expert.

Ask for referrals, and pics of their work.

Find a designer that will listen to your wants and needs, not just a rubber stamp design.

They should understand indoor air quality also, air changes, regulating humidity, etc. You want a comfort system, not just a heating system.

If possible find someone nearby that understands the climate, codes, incentives and rebates and any other aspects unique to your area.

The more reading you do ahead of time the easier to understand and follow the lingo.

www.radiantprofessionalsalliance.org

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_12_0.pdf

www.dsireusa.org is the place to hunt down incentives