Thermally Amazing Shell and System

Mike T., Swampeast MO

Will:

Sorry about that. I keep thinking of the supposed efficiency of the balanced flue model (without the HX). Have made correction. (I used 70% in my calculations)

In this case where space heating was always considered a minor load relative to DHW and other tank-model boilers vastly oversized and any available true boiler requiring a buffer tank plus indirect, a more efficient appliance made no economic sense due to greatly increased equipment costs.

The shell was so efficient that the efficiency of the source that drove it was virtually immaterial. Solar--with it's far lower efficiency--is completely viable in this house with less than 100 gallons of storage.

Conventions do not apply when you are dealing with the unknown and the simple appearance of this system belies the engineering and specification. The circulator is so perfectly suited that the highly suggested replacement is delta-p modulating.

scott markle_2

In my opinion dhw loads alone deserve an efficient appliance. The tank hot water heater will one day find a place in the hall of shame.

I would say if your going to build a house that used almost twice as much wood to enclose the same amount of space as a conventional design why stop with the heating appliance.

Have a look at the sloppy yellow tipped flame with its crude cast iron burner and tell me this is the way we should be burning gas in the twenty first century.

Unknown

it depends on the DHW load. for a couple, it can be fairly small.

Unknown

Energy factor 0.54 is NOT an AFUE rating. it is an efficiency rating for a given (small) amount of domestic hot water usage, assuming a given amount of standby loss through the tank. Standby loss is low, but as a percentage of actual load, it seems high.

As you increase your usage (adding heating), the standy loss remains the same but it becomes a smaller and smaller percentage of the overall use. compare two tank heaters losing 50 BTUs/hr each (made up number). One is used for 1000 BTUs of DHW a day and one is used for 10,000 BTUs of heating per day. that 50 BTUs is 5% of the DHW heater efficiency but only 0.5% of the heating tank efficiency, even though every else is exactly the same.

Recovery factor minus standy loss relatie to usage is a closer number. We use a standing 75% assumption on tank water heaters in heating applications.

Matt_67

When I was in the gas lab, the best combustion efficiency rating we got from a power vented hot water tank, was 74%. This is not AFUE. There is a continuous lost by convestion through the tank which will lower the efficiency of the units.

The local gas utility had maade a big splash of combo units replacing wall units. That was good untill our famous ice storm of 98. The user found that they had no heat during power failures and the gas bill was more than the wal unit and a seperate hot water tank.

I find your design very interesting. It is very good. I would not lower the tank temperature below 140F. Lgeionnaires is a big risk at temperatures lower than 140. Due to this, the tank manufacturerers and CSA have kept the tank minimum temperature at 140 F and suggested a tempering valve at 120F right after the tank.

I can't see what I am writing due to breaking my glasses last night. So, sorry for anyy errors!
Henry