Deltas

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Deltas

Checking delta is one of the most important trouble shooting procedures. This can be Delta P, Delta T, and Delta V. Most common test instruments we use check delta. This includes volt meters, magnahelics/manometers, thermometers, and gauges. Here are some examples of using delta in service are as follows:

Delta P: Checking pressure drop can include water, air, and refrigerant.
Delta T: Check temperature rise/drop across equipment.
Delta V: Check voltage drop on electrical switches to determine the condition of the switch.

Checking refrigerant pressure drop:
There is a direct relationship between liquid refrigerant pressure and temperature. This allows us to use temperature to check for pressure drop on our liquid line. The main use for this technique is to check for liquid refrigerant restrictions. If you suspect a liquid restriction due to high superheat and high subcooling, the next procedure is to check is temperature drop to locate the restriction. This test should be performed with a temperature clamp of the appropriate size for the piping. The best place to start is usually the liquid line drier and all other easily accessible components. If there is no pressure drop from the outlet of the condenser to the inlet of the metering device, the issue will most often be at the metering device. This procedure for trouble shooting is the same for the vapor side of the system, other than the vapor line will have an inverse relationship with temperature. A vapor restriction will cause the pressure to decrease while the vapor line temperature increases. This is due to the reduction in refrigerant volume causing the vapor line to be additionally affected by ambient conditions.

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Thermostat Basics

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Thermostat Basics

There are two common types of thermostat operation, heat pump and conventional.

HEAT PUMP:
Heat pump installation requires selection of either the O or B terminal and a potential requirement of a jumper between W and Y.
The O terminal energizes the reversing valve in cooling and the B terminal energizes the reversing valve in heat. 
If a thermostat has a separate W and Y terminal with no programming selection for heat pump, there is most likely a requirement for a jumper between W and Y.
The programming manual must be referenced to ensure the proper jumper and settings are selected.

CONVENTIONAL:
Conventional system control refers to non mechanical heating such as hot water, gas, electric, etc.
The typical selection options for conventional are gas or electric heat. The difference between the two is how the fan operation is controlled.
With typical gas heat, the fan is controlled by the unit. The gas train fires, ensures complete firing of the gas train. The fan is controlled by the supply air or heat exchanger temperature. Once the system warms up, the fan cycles on. When the system cools, the fan cycles off.
The electric heating option is used for the majority of other heating applications. This includes resistant heat, hydronic, steam, etc.

The most important caveat to all of this is heat pump systems that wire conventional. This is how most Carrier commercial unitary products wire. They are to be wired using conventional wiring with selection for electric heat.

These instructions are only for a brief frame of reference. The thermostat manual should be consulted upon any installation to ensure proper set up.

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Closed Loop Service

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Closed Loop Service

When working with closed loop piping systems there are several critical items to be verified are correct when addressing issues.

Component Selection: When selecting components it is necessary to verify the operating pressure of the system. Some operating conditions exceed the maximum working pressure of standard 150# flanges, valves, vessels, etc. An example of this can be a high rise building where the resting static pressure of the water can be over 150#.

The formulas used to determine the weight of the water are:
2.31’ per linear feet of vertical piping rise = 1 PSIG
.433 PSI = 1 per linear foot of vertical piping rise

 

This math is used to set up the closed loop make up station. The buildings closed loop make up station is used to keep the loop pressurization equal to the resting static pressure requirement based on the total vertical linear pipe run. This is possibly the most overlooked and important component in a closed loop.

Leaks: The enemy of closed loop systems is air. Air in a closed loop can create a hydrostatic condition increasing pressure in the piping system beyond its rated range. Air is also the main cause of corrosion in a carbon steel system. This is also a time where dirt and debris can be easily introduced into the system.

When filling the closed loop the high point vents must be opened and automatic air bleeds removed to prevent air locking any part of the system. If the system allows, the fast fill or make up station bypass may be used at this time until the desired loop pressure is obtained. Once the pressure has been properly set, the fast fill valve should not be touched.

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Scalable Sensor Selection

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Scalable Sensor Selection

When selecting a scalable sensor, transmitter, or switch, we have noticed major issues with device selection.

If an airflow DP switch is selected for most standard unitary products, the design of that system typically operates at no more than 1”Hg with a design of .5”Hg. We have found that installing contractors and service companies typically install switches with a range of .5-10” of Hg. With such a wide scale and the design operation of the system at the absolute bottom of the scale, this makes the switch unreliable at best. Additionally, the older the switch becomes, the more unreliable it will be over time. There are limited applications where the design static of a system will exceed 1.5”Hg, and very little that will exceed 3”Hg.

Example standard static pressure design maximums are as follows:
Unitary Direct Drive Systems 1”
Unitary Belt Driven Systems 1.5”
VAV Type Systems 2”-5” while typically operating between 2-3” with 5” being the max for duct design.

The cause of this is most likely two fold. When technicians call a supplier for parts, they will only ask for a differential flow switch while being ignorant to the fact that a selection needs to be made. The second is that suppliers carry the switches with the largest scale to reduce inventory and serve a greater market with less product on hand.

This is just one specific example of improper device selection. This applies to all device selection. Know your medium and the range in which it will operate and size the device with as tight of a range as possible.

Never rely on the counter guy to know your job better than you. 

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