STP SERIES Install, Operation, and Maintenance Manual
SECTION 3: OPERATION AND CONTROLS
Page
18
of
97
Diversified Heat Transfer, Inc.
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439 Main Road
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Towaco, New Jersey 07082
Rev-1
09/11/2019 PHONE: 800-221-1522
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WEBSITE: www.dhtnet.com
STP Manual
SECTION 3: OPERATION AND CONTROLS
3.1 INTRODUCTION
This chapter provides information and instructions for following topics:
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STP Series functional description
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Preparation of unit for operation
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Unit startup procedure instructions
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Unit shutdown procedure instructions
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Controller overview & startup settings
3.2 STP SERIES FUNCTIONAL DESCRIPTION
DHT’s STP Series units are engineered using boiler water as the heating medium. Heat
exchangers are available in standard brazed plate double wall construction with both simplex and
duplex configuration, depending upon customer requirement for larger capacity or built in
redundancy. STP Series incorporates the proven DHT controls coupled with the high efficiency
brazed plate double wall heat exchangers and variety of storage tank sizes
.
The DHT STP
Series water heater is designed to satisfy potable water heating needs in commercial and
institutional environments. The packaged system utilizes simple, easy-to-understand, real-time
load tracking and responsive controls to maintain accurate hot water temperatures under
various load patterns. DHT STP Series can be coupled with both condensing and non-
condensing type boilers with wide range of operating temperature ranges to achieve high
efficiency within an optimized space. Stored hot water inside the STP tank help to meet the large
instantaneous demand within short period and provide thermal mass for applications requiring
storage. It also helps to reduce the number of cycles on boilers under the periods of no load to
low load conditions and hence eliminate the need for external buffer tank in boiler water piping.
The control system features temperature sensor installed on the storage tank, transmitting a
millivolt signal to PID controller which, in turn sends a 4-20 MA signal to the optional electrically
activated control valves or VFD pumps to achieve accurate temperature control over various
demand situations.
The STP Series can efficiently produce higher flow domestic hot water, depending upon
the temperature rise and available boiler water temperature and flow rate. Skid mounted for
single point connections with a state-of-the-art PID control panel with touchscreen user interface,
brazed plate double wall simplex or duplex heat exchanger configuration, optional electrically
activated two-way control valve or VFD pump and non-ferrous circulator pump.
Easy removal and assembly of heat exchanger and piping via victaulic or union connections
allow the complete removal of the heat exchanger and other pipe components for ease of
service and also help to carry the unit through tight spaces. Isolation valves and backflush
connections provided in heat exchangers piping manifolds for scheduled maintenance.
Cold domestic water enters the storage tank through cold water inlet connection, and hot water
is supplied through connection on top (as shown in Figures 3-1a and 3-1b). If the tank
temperature falls below the set point, water is pumped through the brazed plate heat exchangers
where it is heated with higher temperature boiler water and heated domestic water then exits the
heat exchanger back into the tank. Unit includes constant speed circulation pump(s) which
continuously circulates water through the heat exchanger(s) until tank stored water temperature
is satisfied to ensure there is always hot water present in case of demand. Domestic hot water
temperature is maintained by electronic operated optional straight through 2-way control
valve(s) or VFD pump(s).
Boiler water enters the heat exchanger through the inlet connection located on top of the heat
exchanger and flows downwards to have counter flow arrangement for effective heat transfer.
Optional control valve or VFD pump which is modulated by the 4-20 mA output from the