variable speed blower on water-air HX?

[pybyr]

for folks like me who sometimes do it the hard way.... and in this situation I am referring to using a boiler with a water to air HX over my old hot air oil furnace with a belt drive blower-

can anyone offer any suggestions on whether it might be feasible or sensible to set up a PLC/ PID tied into a VFD to run a 3 Phase motor to maintain maximum net delta-T on the air side of the HX as my "thermal flywheel" heat storage tank varies in temp?

I've got to design and rig some kind of blower control from the house's thermostat and the outlet of the water-air HX anyways, so [in usual glutton for punishment mode] I figure, why not aim for optimal the first time around?

 

[Redox]

Yeah, but it's gonna cost 'ya. Figure on another grand if you want to do it right. Is it really worth it?

It might be more cost effective to retrofit a direct drive blower with an ECM into the furnace instead. Still probably looking at $500 or so.

I never got around to checking on the Evergreen motor for belt drive. Most furnaces are using direct drive for efficiency and reliability nowadays.

Max DT on the water side is going to be at minimum airflow, but this may not be enough to heat the house in cold weather. I think controlling to a set discharge temperature may work better, especially if you incorporate outdoor reset. Many VFDs can do this without any additional hardware.

You might want to take the simple approach on this until you get some more experience with how the system works.

Chris

 

[BrownianHeatingTech]

I think controlling to a set discharge temperature may work better, especially if you incorporate outdoor reset. Many VFDs can do this without any additional hardware.

You might want to take the simple approach on this until you get some more experience with how the system works.

I'll ditto both of those points.

You might be able to deliver more heat with the blower blasting away at full speed, but you'll have a hurricane in your house, and cool air blowing from your registers. There are some situations in which that would be the most "efficient" way to deliver energy, though.

However, the goal of a heating system is not energy transfer - rather, it is occupant comfort. Keeping the discharge air temp at a comfortable level is going to be the biggest factor in that. I can set up a system that blows a lot of 75-degree air into a room, or a little 105-degree air. Because of the "wind chill" effect, the 75-degree air will not feel comfortable, while the 105-degree air will transfer the same energy at a lower flow-rate, and feel more comfortable to the occupants.

And... this is a future project. Get everything else working, first - it's not something that will impact the rest of the system.

Joe

 

[mtfallsmikey]

Just experiment the redneck way: change your sheaves!