Navigation:  Domestic Hot Water Heating > Instantaneous Hot Water Heater
rev. 2008-11-25

Existing Conditions

This facility has high DHW use for <showers> <kitchen> <laundry>, with heat provided by <electric heater tanks> <atmospheric heater tanks> <atmospheric boilers>.

Retrofit Conditions

The existing <heater tank> <boiler/tank combination> should be replaced with one or more <BOSCH>  condensing instantaneous heaters. This system operates at over 90% seasonal efficiency, and has been proven effective even in hard water areas.

The savings come from <substituting expensive electric heat source for a less expensive source (natural gas).  Electricity is approximately three times as expensive as the equivalent heating value of natural gas.> <greatly improving the heating efficiency (from 55% to 90% efficiency).>

Further Benefits

 

 

Application Details

Tankless water heaters that have the lowest energy cost and highest efficiency.

Not only for new facilities.  Be ready to replace failed units with efficient models.  It may even be economical to replace functioning units if they are especially inefficient.  Consider converting to a less expensive energy source.

The BOSCH heater uses plastic (PVC, CPVC or ABS) venting, has sealed combustion, and can vent through a side wall.  Unlike the AO Smith Cyclone, it operates very quietly, and has an excellent turn down ratio (10:1)

Issues and Concerns

 

References

This recommendation is in accordance with Section 7.6 Service Water Heating Systems of the ASHRAE Standard on Energy Conservation in Existing Buildings.

 

Analysis

Use ASHRAE values for gallons per day per bed/person/square foot to establish the first assumption.  Next, input the number of beds or tenants.  The lb/gal is a constant value, and the inlet/outlet temperatures are assumed.

The Mbtu/day is calculated by gal/day x lb/gal x (Temp out - Temp in) ÷ 1000

 

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