Domestic Water Recirculation Systems Part 7: Mixing Valves

RL DeppmannMonday Morning Minutes, Plumbing System Design, Domestic Water Recirculation, Mixing Valves

“Addition of a Mixing Valve” During the last 6 weeks, the R. L. Deppmann Monday Morning Minutes concentrated on re-circulation systems where the supply temperature to the system was the same as the outlet temperature of the water heater. Today we will examine the addition of a Lawler master mixing valve in the system.

Domestic Water Recirculation Systems Part 6: High Rise Considerations

RL DeppmannMonday Morning Minutes, Plumbing System Design, Domestic Water Recirculation, Balancing, High Rise Systems

High Rise Considerations The last article, part 5, showed an example of a high rise system with pressure reducing valves (PRVS) and the importance of the correct setting of the balance valves. The example we used showed balance valves with as much as 18 PSIG across them at a low flow. When a design starts to incorporate

Domestic Water Recirculation Systems Part 4: High Rise Considerations

RL DeppmannBalancing, Monday Morning Minutes, Pumps, Plumbing System Design, Domestic Water Recirculation

The last three articles outlined pump selection in domestic water recirculation systems. In general, these systems have low flow and low head pumps. What happens in a high rise with pressure reducing valves (PRV) in the hot water supply? The pressure reducing valve introduces a fixed pressure drop which must be added to the calculations.

Domestic Water Recirculation Systems Part 3: Pressure Drop

RL DeppmannPlumbing System Design, Domestic Water Recirculation, Domestic Water Recirculation, Monday Morning Minutes, Pumps

The purpose of the domestic water recirculation system is to delivery hot water near a fixture during times when there is no draw. If someone is using hot water in the next room or apartment or process; the hot water is near enough to your fixture so the hot water is delivered in seconds, not minutes.

Plumbing Topic: Domestic Water Recirculation Systems Part 2

RL DeppmannMonday Morning Minutes, Plumbing System Design, Domestic Water Recirculation

Let’s assume the domestic hot water supply is a total length of 1000 ft. That is the entire pipe on all of the floors. Let’s also assume an average of 15 BTU/hr/ft of loss through the supply pipe insulation. Now let’s assume the recirc piping is 300 ft total at an average of 10 BTU/hr/ft of loss. What flow rate is required for a 10 degree ΔT? What flow rate is required for a 5 ΔT?