Combination system for 6 story apartment bldg.

Charles Breidinger

We are considering using a combination space heating and domestic hot water system in our new condo project in San Francisco. The units are all studio type units (350 sf each). The units are stacked for five stories over a garage.

The basic heating concept is to use one hyronic fan-coil unit per dwelling unit. Each fan-coil with thermostat controlled zone valve will be connected to supply and return riser. The boiler(s) with either be located at grade level or on the roof.

The difference between our proposed system and a typical two-pipe hotel system is that we would like to use the supply risers to also furnish potable hot domestic water to the dwelling units. This would therefore be an open system and designed for a 120 deg. F supply temp. to the fan-coils and plumbing fixtures. To eliminate any stagnant potable water issues all zone valves would be cycled once per day via a central timer. The primary benefit would be savings in plumbing costs.

My question for you guys is, has anyone ever seen or installed a system like this and if so, would you do it again?

Thanks for your input.

Heatermon

Seen it ... don't recommend it.

We do repairs for a condo association that has a system simular to what you described. The typical problems we encounter are due to its "open" system design. Without going into the water quality dangers of the system (we'll let PAH handle that), we find most problems are caused by the increased "junk", (lime, calcium, dirt, rust, etc.) that shortens the life of the components (pumps, zone valves, flow switches, air vents,etc.). We also see alot of "nuisance" issues whenever the water is shut off to the building for other types of repairs. When the water gets turned back on, you get alot of air pockets that have to be "burped" from the system. Sometimes it takes weeks to get all the air out because there are so many places it can hide in an "open" system. It may be "cheaper" to install, but I guarantee you, the maintence people will have job security for life. Good luck with your project, but for my money, I would just separate the heating side from the domestic side by using an indiect fired storage tank for the domestic and save myself a bunch of headaches down the road.

Heatermon

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Paul Pollets

El Cheapo es Problemo

While the system you describe would work, it's a very short term solution. I'd use wall panel radiators with thermostatic radiator valves, a high tech boiler and indirect storage DHW tank. Fan coil units aren't very comfortable and make noise (fan noise) which is usually objectionable to most occupants. I don't recommend connecting any high temperature emitter (radiators or FCU's) to a potable water system. Yes, I've seen systems like this. They have high operating costs and maintainence costs.

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Dave_4

sf plumbing code requires double wall hex...

....for domestic water...they also require backflow at the boiler, so i can't see them allowing the open system...

Ted the plumber

domestic for fan coils

I've had problems trying to get comfortable heat from a fan coil with water below 140 degrees, unless you plan on a mixing valve in every unit to reduce the domestic to 120, I really wouldn't recommend it.