Header configuration: Heating
- Dennis De Beuckeleer
- Ruben Gielen
The header configuration library consists of BCs typically used with headers.
Low loss header
The low-loss header is a BC that functions as a hydraulic separator within the circuit. It’s typically used to separate the generation, or production, side from the rest of the circuit. Using a header, you can disconnect the flow rates on the primary & secondary sides from each other. A low-loss header is often used to ensure minimal flow towards the boilers.
A low-loss header is a source for constant flow, and therefore a big contributor to high return temperatures and high pump energy costs. For hydronic optimal purposes, it’s advised to place a low-loss header only when it’s really necessary.
A low loss header has only a few parameters that can be changed:
Primary supply temperature: This is an optional parameter. The Hysopt Optimiser will automatically take over the temperature regime from the secondary gate when calculating the design flows. This calculated value will be overwritten by the parameter value once filled in.
Overwriting the supply temperature has an impact on the subsequent flow calculation further upstream of the primary gate. Note that it’s only possible to fill in higher supply temperatures than the propagated temperature at the secondary gate. If the parameter value has a lower supply temperature, the Optimiser will give an error.
Primary return temperature: This is an optional parameter. The Hysopt Optimiser will automatically take over the temperature regime from the secondary gate when calculating the design flows. This calculated value will be overwritten by the parameter value once filled in.
Overwriting the return temperature has an impact on the subsequent flow calculation further upstream of the primary gate. Note that it’s only possible to fill in higher return temperatures than the propagated temperature at the secondary gate. If the parameter value has a lower return temperature, the Optimiser will give an error.
Filling in both primary supply and return temperatures won’t work, as the flow calculation (q=mcdT) will become impossible. The header will require a mixing point in both the flow and return connection, which is hydraulically impossible.
Primary KV value: The KV value expresses the amount of flow for a pressure drop of 1 bar. By default, this value is set at 1 000 000. In general, the pressure drop over a low loss header is neglectable within the system. If this is not the case, adapting the primary KV value will change the pressure drop over the primary gate.
Secondary KV value: Similar to the primary KV value, changing the secondary KV value will change the pressure drop over the secondary gate.
There are two more BCs that are a variant on the first low loss header and that combine the previous BC with pumps and balancing valves. The parameters that affect the low loss header remain the same. For a more detailed description of the pump & balancing valve parameters, the user is referred to LINK STILL TO MAKE!
Header bypass
Similar to the low loss header, a header bypass functions as a hydronic separator within the circuit. It’s typically used to ensure flow circulation when there is not sufficient demand.
A header bypass is again a source for constant flow, and therefore a big contributor to high return temperatures and high pump energy costs. For hydronic optimal purposes, it’s advised to avoid header bypasses in your system as much as possible.
A header bypass has only one parameter:
Supply temperature: The supply temperature is only needed to make sure the Hysopt calculations can be executed. Make sure to fill in the same supply temperature as in the rest of the system to not trigger any errors in the Optimiser.
There are two more BCs that are a variant on the header bypass.
The header bypass with a non-return valve, depicted on the left, behaves similarly to the header bypass, but has an additional KV parameter to take the pressure drop over the valve into account.
The zero load bypass, depicted on the right, works slightly differently and has one additional parameter affecting the header:
Zero load design flow: The flow rate for which the header is designed to let through when there is no demand. Changing this parameter will not affect the design calculations, but will have an impact on the pipe size selection by the Optimiser.
Overflow
Overflows are header bypasses with valves that affect the flow rate going through. For hydronic optimal purposes, it’s advised that - if a bypass in the system is needed - an overflow system is used and controlled such that the impact of the bypass flow rate on the return temperature and the pumping energy is minimized.
Overflow BCs have the same two parameters as a zero load bypass. They have additional parameters that are linked to the equipped valves. More information about the valve parameters can be found here: Balance valves & Control valves.
Full load vs Zero load overflow
The upper two BCs depicted above may seem similar, but they behave differently. When using a full load overflow, the flow rate filled in at the ‘design overflow rate’ parameter will be taken into account when calculating the flow rates further upstream of the system. When using a zero load overflow, this will not be the case. As a consequence, choosing a full or zero load BC can have a major impact on the design calculations, pipe & optimal component selections further upstream! In general, it’s preferred to work with the zero load overflow, as it will decrease the size of the pipe & pump selections, but the choice should always matched the design philosophy of the installed overflow.
Other overflow BCs
From left to right, the maximal pressure overflow, the pressure independent full load overflow and the pressure independent control valve full load overflow are depicted above. All three have the same overflow parameters as the bypasses explained above. The difference in their behavior is found within the valve parameters. The maximal pressure overflow will open its valve when the pressure exceeds a given overflow setting pressure. The pressure independent full load overflow and the pressure independent control valve full load overflow are two different approaches towards the same block. They keep the pressure over the overflow constant, independent of the flow rate.
Pipe end
The “Pipe end” BC can be used when the user wants to specify a dead-end, reserve/redundant branch, future attachment, …
The functionalities of this BC are limited since it isn’t included in any calculations or simulations. The only parameter available is the supply temperature. The supply temperature is only needed to make sure the Hysopt calculations can be executed. Make sure to fill in the same supply temperature as in the rest of the system to not trigger any errors in the Optimiser.