DESIGN DAY

Mike T., Swampeast MO

Design of 8F this morning. 63F room; 97.4F flue; 96.8F supply; 82.4F return.

Standing iron with TRVs and directly connected Vitodens 200 6-24. Maximum possible flow 6 gpm via the internal circulator.

14.4F delta-t * 500 = 7.2 mbh per gallon of flow

6 * 7.2 = 43.2 mbh maximum possible system output with Manual-J heat loss of 100 mbh @ 8F

I didn't clock the meter, but looked at the exhaust and would say it was less than 40 mbh input--still part lazy.

Unknown

It's a design day (or darn close to it) up here in the northeast.

Great day to take water temperature measurements on systems with water temperature feedback systems... look at boiler cycling patterns... all kinds of fun stuff.

And if you've got any clients who still have some insulating to do, and they aren't a little chilly today... that system is oversized!

Should make design days some kind of holiday... I love 'em.

CC.Rob_4

feedback

2100 sf house full of fin-tube (sized in 1979 for 180F water at probably 0 or 5F) is idling along with ~110-115F water at 15F outdoors. P/S CI boiler doing constant circulation full reset with indoor feedback. Efficient on-cycle and loonnnggg off-cycle.

My painstakingly-detailed Manual J says I should be losing about 40k BTU/hr. Heat input is about 16k BTU/hr and indoor temps are rock solid. Trying to figure out what I'll spend the savings on!

Al Corelli_2

Funny you should mention that

I stopped by my house during the day today to see what goes on.

All calling zones with 17 degree differential.

I think I'm OK.

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Unknown

Now, that's nice. 110 to 115 baseboard under those conditions.. great job on that envelope!!

jp_2

you mean design night.

I have been noticing even on cloudy snowy days I still get solar gain. cabin will stay 10-15F higher than outside temps, once sun goes down it will follow outside temps closer.

my PV panels even collect on very cloudy days.

no real difference than the recent solar collector discussion.

so, true design day conditions will only happen at night.

speaking of, doesn't design day call for certain wind conditions to meet infiltration design losses?

seems if it isn't windy, you are not at design.

scott80

full reset

Hi Rob
Do you mean by full reset is no min on boiler low end? What is the temp at the return of your boiler?I thought you need to keep the water return above 127 for a short time
Thanks

Unknown

If you want to be technical, there is no such thing as a design day.

That said, it is still useful to check system performance when you are approximately at the conditions it was designed for.

CC.Rob_4

windy night

If last night didn't meet design infiltration wind here (if not design temp; and yes, it wasn't blowing from all directions at once like I think Manual J supposes...), I don't know what would. NNW 28-35 kt. I could feel it, and the indoor sensor did, too. Supply temps up a bit over similar temps with lower wind. Neat stuff.

CC.Rob_4

no min

At nearly full load, the dT is around 17F. P/S with VS injection keeps the core hot.

jp_2

big assumption????

isn't it a rather big assumption to think that the variable speed circ is going full bore here?

then to assume it truely is delivering 6gpm? doesn't that value have something to do with headloss of the system?

surely the pump curve is not a horizontal line?

jp_2

sure there is

if your design temp stays the same all day you have a design day!

Mike T., Swampeast MO

Not sure that the circulator is operating at 100% but it has the ability via coding. The HX has considerable head loss and 6.16 gpm is the max the integral circulator can pass through the HX per specs.

21F at 5:00 a.m. input: 31,500 (clocked)

92.4 flue; 91.0F supply; 79.5F return

11.5 * 500 = 5,750 * 6 = 34,500 btu/hr

Boiler reports 100F as "boiler temperature", but with a HX content about 1/250th of the circulating volume, I have a feeling the supply temp I measure about 3' from the HX and found at TRVs from there forward is more representative of the system as a whole.

Over 3 days of continuous modulation since Jan 1 at 1:30 a.m.