A hot water recirculation system prevents this long wait by constantly circulating hot water and to minimise the length of the dead leg.

This means that the loop with the path of least resistance will circulate correctly (at the right temperature), but the water in the other loops, which have more resistance, may barely move (and will be at a wrong/cold temperature).

When you create the pressure zone, you are effectively creating a new hot water recirculation system. This needs a dedicated hot water recirculation pump and heat exchanger.

If you put PRVs on the hot water recirculation pipes it will unbalance the system because of the significant amount of resistance it creates to some loops. See the example below:

Waiting for hot water is tolerable in some circumstances, but a dead-leg system in a large building is not fit for purpose.

"The software offers precision through detailed result outputs and advanced options for efficient pipe sizing, allowing heating engineers to optimise based on parameters like maximum velocity and pressure drop."

So what will the hot water that is being circulated by the pump do? It will take the path of least resistance i.e. the loop with the largest pipes and/or shortest lengths.

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We recommend not moving past this part until 'balancing' makes sense. When it makes sense, the rest of the blog will be easier to follow.

One solution is to put the PRVs on the dead legs that branch off the hot water recirculation system's flow and return pipework.

Although this pump helps us to meet the minimum pressure requirements, we cause a problem elsewhere because the maximum pressures we need to meet too and that is generally around 500 kPa / 5 bar / 80 psi.

Providing multiple dead leg systems is another common way to provide hot water in a high-rise building. They are especially common in apartment buildings, where every apartment has their own hot water plant. A simple diagram is below:

The strategic placement of heat pumps and careful sizing of pipework were crucial in maintaining minimal pressure drops over an 18-metre distance."

By achieving the minimum pressure at the top of the building, you almost certainly exceed the maximum pressure at the bottom of the building.

To meet the minimum pressure requirement in a high-rise building, you will require a pump because water loses approximately 10 kPa / 0.1 bar / 1.5 psi per metre it rises.

CASE STUDIES Award-Winning Heating Design "Using h2x was pivotal, allowing for precise heat loss calculations, pipe sizing and flow rates for each room. This level of detail ensured that the heating load accurately matched each space's requirements, minimising energy waste and maximising comfort. The strategic placement of heat pumps and careful sizing of pipework were crucial in maintaining minimal pressure drops over an 18-metre distance." Read the full case study

CASE STUDIES Salon Republic, USA "The quality of the designs saw significant improvement with the adoption of h2x." "The software offers precision through detailed result outputs and advanced options for efficient pipe sizing, allowing heating engineers to optimise based on parameters like maximum velocity and pressure drop." Read the full case study

"I would estimate over the length of this project, I have spent 50% less time designing than I would on our previous software.

Lets start with understanding the basics of hot water recirculation systems. Have you ever waited a long time for hot water to come out of the tap?

This 3/4 inch pressure relief valve is used in hot water boiler applications to protect against excessive pressure on all types of hot water heating boiler equipment. It consists of a iron body with forged bronze inlet, non-metallic disc-to-metal seating and stainless steel spring. This valve resists corrosive water conditions, sticking and freezing, and prevents water and sediment from being trapped in the seat. It is designed for emergency safety relief and should not be used as an operating control. The pressure setting is 30 psi for applications up to 550,000 BTU/hr.

When a hot water recirculation system is split up into different loops (generally one loop per level), each loop usually consists of different pipe sizes and lengths.

Simply draw the layout of the hot water system, set your design parameters, and all of the hot water recirculation calculations will be undertaken.

CASE STUDIES Greengate, UK "I would estimate over the length of this project, I have spent 50% less time designing than I would on our previous software. The ability to output the design straight into Revit assisted clash detection and coordination." Read the full case study

Once the resistance is equal in each loop, the system is 'balanced', and the hot water will circulate equally (at the right temperature).

This level of detail ensured that the heating load accurately matched each space's requirements, minimising energy waste and maximising comfort.

It is commonly thought that a better solution would be to put one PRV per level on the hot water recirculation system's flow and return pipework. You should not do this.