Chapter 4 Applications for the heat pump configuration
14 CNT-SVX06B-EN
Binary inputs for water-source heat
pump applications
The Tracer ZN511 zone controller includes five binary inputs. Each
binary input associates an input signal of 0 Vac with open contacts and
24 Vac with closed contacts. Table 3 gives the function of each binary
input for water-source heat pump applications. Each function is explained
in the succeeding paragraphs. For an explanation of the diagnostics gen-
erated by each binary input, see “Diagnostics” on page 62. For more infor-
mation about how the controller operates, see Chapter 5, “Sequence of
operations for the heat pump configuration”.
BI1: Low-temperature detection (circuit 2)
The function of low-temperature detection is to protect a heat exchanger
from freezing. BI1 is used to protect the second heat exchanger in a two-
compressor unit. If BI1 is wired to a binary low-temperature detection
device (freeze-protection switch), the ZN511 will detect a low-tempera-
ture condition and generate a Low Temp Detection Circuit 2 diagnostic.
Low-temperature detection for the first heat exchanger is always done by
AI1 (see “AI1: Leaving water temperature” on page 20).
Table 3. Binary inputs for water-source heat pump applications
Binary input
terminal label
Function
BI1 Low-temperature detection
BI2 Condensate overflow
BI3 Occupancy or generic binary input
BI4 and V4 High and low pressure cutout (compressor 1)
BI5 and V5 High and low pressure cutout (compressor 2)
Note:
Some heat pumps have a safety circuit to protect the unit. This
circuit contains the compressor contactor, a lockout relay, and
unit safeties (Figure 5 on page 17). These safeties may include
a freeze-protection switch. For the Tracer ZN511 to generate a
Low Temp Detection Circuit 2 diagnostic, the freeze-protection
switch must be removed from the safety circuit and wired
directly to BI1. If the application does not warrant the use of
BI1, configure the input as Not Used. Diagnostics for this func-
tion will not be generated; however, units with a safety circuit
containing a freeze-protection switch will maintain their exist-
ing level of freeze protection.
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