ASHRAE 90.1-2010 Table 7.8 Hot Water Supply Boilers

[PEDARRIN2]

Looking at the table for hot water supply boilers (for domestic water heating), there is a criteria which indicates >= 10 gal. Part of the requirements is calculating the standby loss.

How can a hot water supply boiler (assuming this means a side arm type) have more than 10 gallons of water in it? I would assume this would make it a storage water heater which is covered in another part of the table and the standby loss calculation matches.

I don't think it is referencing the accompanying storage tank. The energy efficiency of those is covered in another part of the table.

Anybody run into this?

 

[lilliput1]

Standby loss would include heat loss through piping, heating coils, expansion tank etc so system volume is required,

 

[PEDARRIN2]

lilliput1,

What is the basis in the ASHRAE Standard for referencing volume as the system volume and not the water heater volume?

Note a of Table 7.8 indicates V is the rated volume in gallons. In the 90.1-2013 User's Manual, all the examples use the water heater volume, not any piping/equipment volume. The loss of heat in the piping system is covered elsewhere.

 

[ChasBean1]

Either that is a horribly asked question or I am severely mentally challenged...

 

[PEDARRIN2]

ChasBean1

Which question are you referencing?

The original query or the reply to lilliput1?

 

[dbill74]

ASHRAE defines a hot-water supply boiler as:

a boiler used to heat water for purposes other than space heating.

I read this as including storage and non-storage type boilers.
The volume requirement would seem to make the requirement relevant to storage type boilers.
Your side arm or non-storage type boiler would then not be required to meet the table's standby losses. However, the storage tank it is feeding would need to have R-12.5 insulation in accordance with this table.

 

[PEDARRIN2]

Then what is the difference between a gas storage water heater (with load >= 200,000 BTUH, and >= 10 gallon) and gas hot water supply boiler with >=4,000 BTUH/gal and >= 10 gallons?

Both are categories in the chart.

I remember there used to be a designation given to "boiler" as having an input >=200,000 BTUH, but that could be storage water heaters as well.

 

[dbill74]

water heater: vessel in which water is heated and is withdrawn for use external to the system.

Also

WATER HEATER. Any heating appliance or equipment that heats potable water and supplies such water to the potable hot water distribution system.

The way I see the difference (my interpretation of the definitions) is based on their use. A water heater is used for heating water in a potable hot water system, maxing out around 140°F.
A hot water boiler would be for generating hot water or steam used for some other process. I.E. boiler used to generate steam for a dry cleaning service.

 

[PEDARRIN2]

The issue I have with that differentiation is Chapter 7 of the ASHRAE Standard is for "Service Water Heating", which according to the ASHRAE Handbooks, is differentiated from equipment used for space conditioning.

So, a hot water boiler, in the table would not be for some other process.