Commercial Water Heaters
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 3
to Rev 4
in Commercial Water Heaters.
---
title: Commercial Water Heaters
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```
−### The Contractor shall submit the action submittals listed above for the Engineer's review prior to procurement and installation.
−
−### Work shall not proceed on any water-heating equipment until the corresponding submittals have been reviewed and returned.
−
## Closeout Submittals {toc}
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### Fuel-fired water heaters require combustion air at a rate determined by the input rating of the heater and the venting category. {note}
+### The combustion air source shall be specified for each fuel-fired water heater, consistent with its input rating and venting category, or designated not applicable for electric or heat-pump units.
+
```datasheet
label: Combustion Air Source
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### Domestic-water inlet water quality affects the service life of all wetted components, particularly anode rods, glass-lined tank linings, and brazed-plate heat exchangers in indirect-fired equipment. {note}
+### Where the inlet water hardness exceeds 7 grains per gallon (gpg), softening or scale-control treatment shall be evaluated by the Engineer.
+
```datasheet
label: Inlet Water Treatment
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```
−### Where the inlet water hardness exceeds 7 grains per gallon (gpg), softening or scale-control treatment shall be evaluated by the Engineer.
−
### Where the chloride level exceeds 100 mg/L or the water is supplied by an on-site well of unknown chemistry, the tank lining material shall be selected for the water chemistry (stainless steel 316L for high chlorides; glass-lined for typical municipal supply; cement-lined for very large indirect tanks).
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### The input rating governs the recovery capacity and the standby losses of the equipment. {note}
+### The input rating shall be [[drawing: as indicated on the water heater schedule]]; the datasheet establishes the typical input rating ranges, and the Engineer's calculation governs the actual selected value.
+
```datasheet
label: Heater Input Rating — Gas
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```
−### The input rating shall be [[drawing: as indicated on the water heater schedule]]; the datasheet establishes the typical input rating ranges, and the Engineer's calculation governs the actual selected value.
−
## Recovery Capacity {toc}
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### Gas-fired water heaters are classified by venting category under ANSI Z21.10.3 and NFPA 54 by combustion-system pressure (positive or negative within the vent) and by the dew point of the flue gas (above or below). {note}
+### The vent category of each gas-fired water heater shall be specified in accordance with ANSI Z21.10.3 and NFPA 54, based on its combustion-system pressure and flue-gas dew point.
+
```datasheet
label: Vent Category
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## Heat-pump water heaters (HPWHs) extract heat from ambient air and reject it into the stored water, achieving COP values of approximately 2 to 4 depending on ambient conditions. {note}
−```datasheet
−label: HPWH Source-Air Configuration
−type: select
−options:
− - "Ambient air drawn from mechanical room (room must be sized adequately)"
− - "Ducted from outside — supply and return ducts"
− - "Ducted from outside — supply duct only with mechanical-room exhaust"
− - "Split-system with outdoor compressor and indoor storage tank"
− - "Not applicable — not HPWH"
−default: "Ambient air drawn from mechanical room (room must be sized adequately)"
−```
+## The backup heat source, or the absence of one, for each heat-pump water heater shall be specified.
```datasheet
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## The HPWH source-air space shall be sized large enough to avoid driving the supply ambient below the unit's minimum operating temperature.
+```datasheet
+label: HPWH Source-Air Configuration
+type: select
+options:
+ - "Ambient air drawn from mechanical room (room must be sized adequately)"
+ - "Ducted from outside — supply and return ducts"
+ - "Ducted from outside — supply duct only with mechanical-room exhaust"
+ - "Split-system with outdoor compressor and indoor storage tank"
+ - "Not applicable — not HPWH"
+default: "Ambient air drawn from mechanical room (room must be sized adequately)"
+```
+
## HPWH condensate generated by dehumidification of the source air shall be piped to a drain.
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# Recirculation System {toc}
−## Purpose {toc}
+## In commercial buildings, domestic hot water must be delivered to fixtures within a time that satisfies both occupant comfort and the energy code.
−### In commercial buildings, domestic hot water must be delivered to fixtures within a time that satisfies both occupant comfort and the energy code.
−
```datasheet
label: Recirculation System Configuration
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```
−### Without a recirculation system, water in long horizontal branches stagnates, cools, and creates conditions favorable to Legionella in the dead leg; the recirculation system keeps water circulating continuously or on a controlled schedule through a return loop from the distribution piping back to the water heater, maintaining the return temperature above the Legionella threshold throughout the loop. {note}
+## Without a recirculation system, water in long horizontal branches stagnates, cools, and creates conditions favorable to Legionella in the dead leg; the recirculation system keeps water circulating continuously or on a controlled schedule through a return loop from the distribution piping back to the water heater, maintaining the return temperature above the Legionella threshold throughout the loop. {note}
−### The return-loop piping itself is the scope of [[sync/domestic-water-piping]]; this standard establishes the pump, control, and balancing requirements at the equipment. {note}
+## The return-loop piping itself is the scope of [[sync/domestic-water-piping]]; this standard establishes the pump, control, and balancing requirements at the equipment. {note}
## Recirculation Pump {toc}
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### ASHRAE 90.1 requires that recirculation pumps not operate continuously when there is no demand. {note}
+### Control shall be by aquastat (return temperature sensor), time clock, demand-based trigger, or a combination, as required by the energy code in force and the building's operating schedule.
+
```datasheet
label: Recirculation Pump Control
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```
−### Control shall be by aquastat (return temperature sensor), time clock, demand-based trigger, or a combination, as required by the energy code in force and the building's operating schedule.
−
### Combined aquastat-plus-time-clock control is the most common commercial configuration — the time clock disables the pump during unoccupied hours, and the aquastat cycles the pump within occupied hours to maintain return temperature only when needed. {note}
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### Where the recirculation loop serves multiple branches or multiple risers, balancing is required so flow is proportional to the heat loss of each branch rather than taking the path of least resistance. {note}
+### Where the recirculation loop serves multiple branches or multiple risers, balancing valves or pressure-independent automatic balancing valves shall be provided at each branch take-off or riser base on the return circuit to ensure flow is proportional to the heat loss of each branch.
+
```datasheet
label: Recirculation Balancing Method
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```
−### Where the recirculation loop serves multiple branches or multiple risers, balancing valves or pressure-independent automatic balancing valves shall be provided at each branch take-off or riser base on the return circuit to ensure flow is proportional to the heat loss of each branch.
−
### Without balancing, the shortest-path branches circulate at excess flow while the longest branches stagnate, defeating Legionella control in the dead legs. {note}
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## The Contractor shall deliver the spare parts listed above to the Owner at substantial completion, marked with the equipment identifier and stored in a labeled container in the mechanical room or a location designated by the Owner.