Optimal temperature settings

Halbert

Last spring I converted my hot water baseboard system from fuel oil to natural gas. As part of the project, the contractor added a buffer tank to limit the short cycling. The system has 3 zones, two of which are fairly small. So far so good now that we're in heating season. It looks like the cost savings on fuel will pay for the project in a couple of years. The system has 2 circulating pumps, one from the buffer tank up to the house, and one between the boiler and the buffer tank. Now comes the question:

The buffer tank thermostat is set at 165F, the boiler aquastat is set at 185F with a 20F differential. Here's the question: which one determines the hot water temperature that is heading up to the baseboards? It seems to me that the actual operation has the boiler functioning to keep the buffer tank at it's set temperature (165F), and the incoming temperature at the baseboards is never going to be the 185F, which historically was needed to keep the house at 68 on the coldest days.

Am I missing something?

Jamie Hall

No. you're not missing anything -- and you may need to raise the buffer tank temperature when it gets colder.

hot_rod

It could depend on how you piped the buffer. If it is piped like this with 4 connections, there will be some temperature blending in the tank. Unless the flow rate is identical, then the temperature from the boiler would go to the heat without a temperature change. If you have multiple zones with a 4 pipe, there would be blending based on flow rates.

Halbert

Thanks for the comments. It is a 4-pipe configuration, so I can see how some blending will happen. We shall see what happens if it gets really cold this winter (I'm in suburban Philadelphia, so even 10F is rare here). I'm really grateful I'm not paying $6 a gallon for fuel oil.

hot_rod

Halbert said:

Thanks for the comments. It is a 4-pipe configuration, so I can see how some blending will happen. We shall see what happens if it gets really cold this winter (I'm in suburban Philadelphia, so even 10F is rare here). I'm really grateful I'm not paying $6 a gallon for fuel oil.

See how it works.

There is another way to pipe a buffer tank so you eliminate that blending. It's called direct to load piping.