Is there a difference between the primary and secondary loop?
Not a thing. The flow from the primary pump (100 GPM) is going straight through both tees and the water in the secondary loop is just sitting there. All the action is in the primary loop. This is the basis for another common hydronic rule: in the other if there is no pressure drop in the piping common.
What is a secondary loop refrigeration system?
A secondary loop refrigeration system incorporates two different refrigerants to provide cooling. In all systems, the primary loop is a traditional direct expansion design that uses a phase change refrigerant such as R-404A and a compressor to circulate the refrigerant. This primary fluid is typically restricted to the machine room.
What is primary loop piping?
Primary Loop Piping also works well with condensing boilers allowing proper flow through the boiler for the highest rate of heat delivery. Primary Loop with one temperature the same as the Heat Source and one temperature that can be lowered
What are the benefits of secondary loop systems?
In doing so, the benefits of secondary loop systems in comparison to other alternatives will be evaluated. This analysis will show that secondary loop systems are not only environmentally friendly, but they have a low initial cost, simplified piping, low cost of operation and are easy to maintain.
What is the purpose of a primary-secondary loop?
Primary-secondary pumping lets you use small, inline circulators - even on large commercial jobs - and that's a real plus. And in a multiple-boiler system, this simple method of piping gives you a way to lower boiler standby losses and save fuel.
What is a primary loop?
Primary Loop Piping is commonly used in boiler heating systems that run needing multiple temperatures or contstant temperature at the hydronic boiler is required. Primary Loop Piping allows non condensing boilers to maintain a heat level in the boiler high enough to allow the boiler to run at its most efficient state.
What is primary and secondary pipework?
What is a Primary-Secondary Piping System? The Primary-Secondary piping arrangement includes two sets of pumps, system pumps and boiler pumps. The system pumps distribute water to the terminal units and the boiler pumps circulate water through a loop that serves the heating equipment only.
What is primary and secondary pump in chiller?
Primary pumps are tasked only with maintaining constant flow within the primary chiller circuit. The secondary pumps (usually fitted with VFDs) maintain variable flow as per real-time load conditions in the secondary chilled water circuit.
What is a secondary heating system?
Secondary heating systems are those that provide space heating which is in addition to that provided by the main heating. This report considers two types of secondary heating: § Alternative heating: defined as heating that is used instead of the main heating in a room.
What is a primary flow pipe?
The coil, or "heat exchanger" forms part of the central heating circuit, and its water heating abilities are purely a by-product of its main function, which is to heat the radiators. This heating is called the "primary" circuit, the pipes running to and from the boiler are called the primary flow and return.
How do we typically control pressure on the secondary loop?
By throttling this valve, we create a pressure drop through the common pipe, which forces more water into the distribution piping. The control valve is the only means of control in this type of system.
How does a secondary return work?
Secondary Returns—These are used to avoid excessive water draw off before the hot water at the tap is at the correct temperature. Heat Pumps and Secondary Returns—Any pumped return promotes mixing, destroying stratification within the hot water tank.
How does a boiler loop work?
The loop works like a siphon that runs out of water. The point where the loop connects to the equalizer is higher than the boiler's crown sheet and that's what provides the safety. Since the water couldn't instantly vanish from the boiler, it bought the Dead Men some time to notice the problem and save the boiler.
How do primary and secondary pumps work?
The primary loop uses a constant speed pump to circulate the working fluid (water). The secondary loop uses a variable speed pump to manipulate the flow of the fluid such that the cooling coil demand is satisfied. The above mentioned pumps are considered as a primary/secondary pumping pair.
What is a primary and secondary in HVAC?
The primary loop is dedicated to the chillers, and the secondary loop is dedicated to the loads in the building. One of the main reasons behind using this pumping approach is the sensitivity of the chillers to variations in the water flow through the chiller evaporator bundles.
What are the advantages of primary secondary systems?
As a result, primary/secondary pumping offers two important advantages: Less energy is required to move water through the entire system (rather than one large circulator, small energy-efficient circulators can be used to overcome the friction and inertia—or pressure drop—of their respec- tive loops).
What is a boiler loop?
A boiler filling loop is a tool used to provide a temporary connection between the boiler and the mains water supply, allowing you to re-pressurise your boiler and fill your heating system with water.
How does a circulating pump work on a boiler?
A circulating pump is a water pump that moves hot water around your heating system. The water travels from your boiler through to the pipes that feed your radiators, towel rails, and hot water cylinder. The water then flows back to the boiler to maintain a constant flow of heated water around your home.
Does pump go on flow or return?
The best place for the pump(s) is still on the flow side. This keeps the bulk of the system under positive pressure from a combination of the pressure imposed by the system water connection, and then when the pump is running, the pressure provided by the pump.
How do closely spaced tees work?
If you are going to build a true primary/secondary system, each load circuit and each heat source needs to connect to the primary loop using a pair of closely spaced tees. These tees isolate the pressure dynamics of each circulator from the other circulators in the system. This is called hydraulic separation.
BASIC APPROACH
The white paper provides details on both the basic secondary refrigeration system and a two-phase variation. Here’s the technical details given for the more basic approach:
TWO-PHASE SECONDARY LOOP
The white paper described a two-phase secondary loop as a “variant, which uses a two-phase mixture as the refrigerant.
Manifolds and piping
Manifolds that accept large-diameter feed pipes from a pump unit are the preferred method for splitting the flow of water to smaller diameter pipes or hoses that are routed to individual heat exchangers. Manifolds must be constructed of materials compatible with the pump unit and related piping.
Flexible hoses and connections to manifolds and heat exchangers
Pipes and hose configurations can vary and are determined by analyzing the needs of your facilities, or a site preparation representative can provide this analysis.
What is secondary loop?
The secondary loops in my case serve smaller air handlers in one building. The primary loop runs through the heart of the building, the secondary or other loops run off, or are tapped off the primary. Depending on load and cooling needs you may increase pump speeds or add pumps to increase flow.
What control package is used for variable flow evap?
For you variable flow evap folks, have the chiller control package in control of the primary VFD, or you'll be in surge city.
Can you reverse flow a HX secondary?
Then add the fact you can use reverse flow at the HX secondary's common pipe connection with the primary and have different medium temps delivered to the terminal units.
Is a P/S system a primary or secondary loop?
Subdividing various systems into a primary /secondary (P/S) loop via a hydraulically dependant interconnection long has been a standard solution for central chilled-water plants in the United States and Europe. This achieves, at a relatively low cost, reasonably good hydraulic separation of central-water-plant cooling-generation systems (primary loop) from distribution piping and terminal units (secondary loop). Primary-loop flow is relatively constant, while secondary-loop flow varies based on load demand. Primary- and secondary-loop water flows are interchangeable.
What is primary loop piping?
Primary Loop Piping is commonly used in boiler heating systems that run needing multiple temperatures or contstant temperature at the hydronic boiler is required. Primary Loop Piping allows non condensing boilers to maintain a heat level in the boiler high enough to allow the boiler to run at its most efficient state.
Does primary loop piping work with condensing boilers?
Primary Loop Piping also works well with condensing boilers allowing proper flow through the boiler for the highest rate of heat delivery.
What happens if you add a pump to a secondary loop?
So what happens if we add pump to the secondary loop? A secondary pump will establish flow in the secondary loop whether a balancing valve is present in the common pipe or not. In this case, we’ve installed a secondary pump that is generating 150 GPM of flow in the secondary circuit. Meanwhile, we still have just 100 GPM in the primary loop. Going back to the Tee Law, we know that you can’t have 100 GPM going in the Tee and 150 GPM coming out. So where is the other 50 GPM coming from?
Does the Tee Law work in reverse flow?
For now, it is important for you to understand that the Tee Law holds true, even if it means creating a reverse flow situation. Again, without a pressure drop (balancing valve) in the common pipe, the flow through the primary and secondary loops will remain independent of each other.
What is the output of a secondary controller?
The output of the secondary controller is used to adjust the control variable. Generally, the secondary controller changes quickly while the primary controller changes slowly. Once cascade control is implemented, disturbances from rapid changes of the secondary controller will not affect the primary controller.
Why is the inner loop chosen?
The rationale behind this example is that the steam in flow can fluctuate, and if this happens, the flow measured by FC1 will change faster than the temperature measured by TC1, since it will take a finite amount of time for heat transfer to occur through the heat exchanger. Since the steam flow measured by FC1 changes at higher frequency , we chose this to be the inner loop. This way, FC1 can control the fluctuations in flow by opening and closing the valve, and TC1 can control the fluctuations in temperature by increasing or decreasing FC1 set .
What is a single input, single output system?
In the previous chapters, only single input, single output (SISO) systems are discussed. SISO involves a single loop control that uses only one measured signal (input). This signal is then compared to a set point of the control variable (output) before being sent to an actuator (i.e. pump or valve) that adjusts accordingly to meet the set point. Cascade controls, in contrast, make use of multiple control loops that involve multiple signals for one manipulated variable. Utilizing cascade controls can allow a system to be more responsive to disturbances.
How to maintain a smooth flow of information in a cascade?
In order to have a smooth flow of information throughout the control system, a hierarchy of information must be maintained. In a double loop cascade system, the action of the secondary loop on the process should be faster than that of the primary loop. This ensures that the changes made by the primary output will be reflected quickly in the process and observed when the primary control variable is next measured. This hierarchy of information can be preserved by applying the following conditions when setting up the cascade controls.
Can a cascade have multiple loops?
In addition to this common architecture, cascade control can have multiple secondary loops; however, there is still one primary loop and a main controlled variable. Unfortunately, with multiple inner loops, tuning the PID becomes even more challenging, making this type of cascade less common.
Is a cascade loop closed loop?
Although cascade control generally incorporates information from several secondary loops, the system overall does not automatically become a closed loop or an open loop process. For a cascade control to be open loop, all control loops in the system should be open loop in nature. On the other hand, if any of the control loops in the system is feedback-based, the system overall is considered as closed loop. This is due to the fact that the system is getting some sort of feedback, no matter how little the “fedback” variable influences the system.
