Installation guide

10 | Rinnai Continuous Flow Water Heating Specication Guide 02-13
Specifying commercial solutions
Rinnai Infinity HD/EF units, manifolded units (joined together), Demand Direct, Demand
Duo, and Demand Rapid can provide all the hot water for large demand applications such
as sports clubs, restaurants, motels, and apartment projects.
For full details on Rinnai’s Demand
solutions, please refer to the
Commercial Water Heating
catalogue available on our website
www.rinnai.co.nz/waterheating_
brochures.html.
Considerations when specifying
commercial solutions
- Requirement for endless hot
water or demand over a short
period
- Water pressure and flow
requirements
- Capital cost limitations
- Running costs
- Positioning of units (external/
internal)
- Flueing options
- Gas supply and availability
- Space restrictions for siting
units
For standard commercial
applications there are two types
of methods that can be used for
determining a hot water solution.
- Continuous flow
Provides hot water endlessly at
a constant temperature up to a
maximum flow rate.
- Average demand
Provides an unlimited flow
rate, but there is a limit to
the total volume of hot water
(litres) that can be delivered
over a time period, i.e. one
hour.
Continuous flow
This application is used when the
demand involves all of the draw off
points connected, usually at the
same time. Typical applications are:
- Restaurants
- Car washes
- Laundries
- Food processing plants
- Caravan parks
- Correctional facilities
The demand can be easily
calculated by totalling the full
flow from all the outlets used. For
example, eight showers at 12 litres
per minute equals 96 litres per
minute.
Average peak hour demand
This method applies when the use
of draw off points occur as purely
random events over the demand
period. Typical applications are:
- Apartments
- Hostels
- Hospitals
- Retirements villages
- Hotels and motels
The demand for hot water is
dependent on the following:
- Occupancy classification of
the building
- Number and type of hot water
outlets
- Number of persons
accommodated
- Time of day
Due to the diversity of hot water
use in these applications the use
of Rinnai Infinity units coupled
with secondary storage may be
required to meet peak demand.
Electronically manifolded units
with primary flow and secondary
hot water return pipe work could
also be viable.
Hot water demand =
(shower flow rate) x (cold water temperature rise to mixed)
(temperature rise from inlet to Infinity outlet temperature)
Continuous flow worked example
A sporting facility change room has ten showers and six basins. The showers have shower roses with a flow capacity of
12 L/min, and the showering temperature is assumed to be 42 °C. The use of the basins is intermittent so they are not
included in the calculation. The incoming water temperature is 15 °C.
1. Calculate the maximum simultaneous demand.
10 showers x 12 L/min = 120 L/min of mixed water at 42 °C
2. Calculate the hot water demand for the shower heads based on a mixed flow rate, using the calculation below.
120 x (42-15)
50-15
= 92.6 L/min (1.543 L/sec)
3. Calculate the heating capacity required.
1.543 L/sec x 4.2
(kJ/kg energy required to heat 1 kg of water 1 °C) x (50-15) = 226.8 kW is required
Five Rinnai Infinity HD200 units, with an output of 47 kW each, could be manifolded together to meet this application.