Bad idea to use a too big heat exchanger?

[TSN79]

I'm constructing a water based central heating system, and in it is a plate heat exchanger. People often tell me not to be scrimpy regarding its effect when picking one. But then I've heard others say that having a 150 kW heat exchanger - when the effect needed will never rise above 40 kW - is perhaps an even worse idea. Could someone give me some point about why it's a bad idea so I can relay?

 

[russ_watters]

It depends on the application. Often it is a significant benefit (lower pressure drop, more efficient heat exchange). When you say a "water based central heating system", what exactly do you mean? What is the heat source that heats the water via the plate heat exchanger?

An example where too big is a bad idea is a heating coil in a 100% outside air handling unit. Too big means low fluid velocity, means uneven surface temperature, means you can freeze the water in the coil even when it comes in very hot.

 

[TSN79]

When you say a "water based central heating system", what exactly do you mean?

The hottest side of the exchanger comes from a district heating system (120°C supply). The other side consist of a normal radiator system (supply/return 70-50°C).

 

[russ_watters]

Oh, just water to water: Bigger is better. Just make sure you appropriately size any pumps or control valves .