Is this set up okay

Mark Eatherton

it is definately not the wisest use of the equipment supplied. This biggest stumbling block is the use of fan coil units (hydro air). Most hydro air units have a limited coil surface size, which requires a higher supply temperature in order to deliver comfortable heat. The manufacturers of the coils actually have a Thermo Snap Disc connected to the outlet of the coil to insure that adequately hot water is present before the fan is allowed to turn on. Some are adjustable, some are not.

Possible solutions include the use of a variable speed fan, that has the ability to run based on coil delta T (expensive and not readily available) or turn the Thermo Snap Disc temperature setting to a lower threshold.

The snap disc could be eliminated, and a relay wired in parallel to the call for heat to start the fan immediately, but again, this may cause discomfort for anyone sitting near a vent termination because the air temps coming out of the coil may be near or below human skin surface temperature. Possibly the addition of a time delay relay to allow hotter water to get to the coil, prior to starting the fan, may alleviate this condition.


As for boiler operation, the boiler will still modulate, but may not condense a lot at that elevated temperature. Modulation, in and of itself will produce fuel savings over the typical ON/OFF appliance, but not as much as the appliance could save if it were operated in condensing mode. It may require some experimentation, but I think there is probably a happy medium, whereby the outdoor reset can be connected and programmed to allow efficient and comfortable operation.

Most off shelf contractors are worried about getting the dreaded "cold customer call", and will set the system up conservatively to avoid that call. They're (contractor) not paying for the gas bill, and in the case of a new home, who is to say it (fuel bill) is high. Higher than what? No track record has been established.

I have personally been able to reduce fuel consumption by up to 30 percent just by tweaking controls on systems installed by another contractor.

ME

Jim_143

does this set up seem ok?

A friend of mine has a new 4000 sf house with a W/M ultra 240 boiler. He has radiant heat in the finished basement and hydro air in the 2 upper floors. He doesn’t have the outdoor reset hooked up. The output temp on the boiler is set high, 185, and he has a mixing valve on the supply to the radiant to lower the temp down to around 110. This doesn’t seem like the most efficient set up to me. Is there anything he can do to increase his efficiency?
Thanks

Jeffs bro

Thanks Mark

Is the ultra able to set more than 1 zone on high temp? I know the DHW zone is set to high and has priority, I was wondering if the 2 zones in the basement can be set up diffrently, low temp.
Thanks

Mark Eatherton

I don't think so...

Most boilers have one reset curve. You can then mix o different temperatures below that point using any off shelf mixing systems, but the boiler has to cover the worse case scenario.

The only boiler I am aware of that can do anything close to that is the Viessmann Vitodens, and even it requires more add on controllers to generate numerous water temperatures.

ME