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:

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.

Recirculating hot water systemdiagram

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).

Hot water recirculatingpump

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

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

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.

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

Recirculating hot water systemretrofit

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

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Hot water recirculatingpump installation diagram

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.

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.

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.

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

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

Hot water recirculating systemwith dedicated return line

"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."

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?

How does ahot water recirculating systemwork

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.

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

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.

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

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

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

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:

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

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