consolidating two heat zones into one

ljb

I recently had a new multizone HVAC system installed on a second floor; it now uses one air handler and one large compressor (4ton) with a zone controller for four rooms. I previously had two air handlers and two air handlers.

Well, the installer also removed both heating coils and installed one new coil. However, only one of the zones from the boiler now supply hot water for this bigger coil. The other zone at the boiler was just disconnected.

I am worried I don't have enough heat energy going to second floor heating coil.

Any input appreciated.

CMadatMe

Heat Loss

Where's the heat loss? That is going to tell you the needed output of the coil to overcome the loss. A 4 ton hydro coil is pushing 70,000 plus btu's at 180 degree water temp. Need to know the loss of each zone, water temp feeding the air handlers as well as its make and model to know it's actual capable output. Did we change any duct work?

ljb

answer

I was not told how big the new heating coil is. Airhandler is a Lennox 5 ton (i believe) variable speed...CBX32MV-060.Propane fired boiler with a 7/8" copper pipe supplying hot water to the new second floor coil.  Duct work was adjusted to reflect a four zone system (four main rooms) from a prior two zone system.I should add that I believe that the installer did not perform a Manual J calculation, and did this by estimation. The total floor area being heated/cooled is about 2200 sqft, with two rooms having 9 foot celings and two vaulted at up to 15 ft.THX!

CMadatMe

Heat loss

A heat loss is the math forumla that the installer uses so he can properly size the equipment. It is a formula that tells us the amount of heat the home needs on the coldest day of the year.



Looks like a 5 ton a/h. Unfortunately to answer your concern need the heat loss and hw coil model. Then need to know the make and model of the boiler to see if it can deliver the needed btus to the coil.

ljb

answer

See edits to my prior text. I dont believe they ever did a Manual J calculation, but see dimensions. Probably "malpractice". It is a ceder shingle two story house with insulated second floor ceiling and attic...multiple traditional windows. Heater is Weil McClain 550223807/0196WM...propane fired.

CMadatMe

If Anything

Based on what you've posted it maybe oversized. The coil was probably just matched to fit on the air handler. If that is the case then you probably have a HW coil that has the capability to push around 90,0000 btus. Don't know what part of the country you are but in a zero degree climate with R-19 walls, R-30 attic and decent windows I would say the total heat loss is in the 50,000-60,000 btu range. This is a conservative number.

CMadatMe

If Anything

Based on what you've posted it maybe oversized. The coil was probably just matched to fit on the air handler. If that is the case then you probably have a HW coil that has the capability to push around 90,0000 btus. Don't know what part of the country you are but in a zero degree climate with R-19 walls, R-30 attic and decent windows I would say the total heat loss is in the 50,000-60,000 btu range. This is a conservative number.

ljb

answer

We live in Eastern Long Island, NY. So are you saying the BTU's for second fllor heat will be sufficient in winter? And is the BTU's delivered from the single 7/8" hot water pipe sufficient?

CMadatMe

Not Saying

That. Pipe feeding the coil is 3/4" copper which is 7/8 od. Would rather see 1" copper. Not sure if 3/4 is big enough to move the require gpm because I don't know whose coil it is and the model as well as don't know the true heat loss.



I do know that I need 1" pipe to move 6gpm or 60,000 btus on a standard 20 degree delta-t.

ljb

Much Appreciated

This has been helpful. I understand the problem better now.

Greg Maxwell

W/A

Please call the ins talling contractor, have him come back, and explain his reasons for installing your system the way he did.

ljb

Follow Up

We finally had a Manual J completed and and the heat loss is 65,400 BTU. I believe you said that you thought that a 1" OD pipe would supply enough hot water for a 60,000 heat loss level. Sounds like we have an issue...

ljb

FOLLOW UP QUESTION and DETAILS

We did some more research.



Our contractor gave us this document from the Hydronics Institute Handbook. You can see a BTU rating for the 3/4" pipe of 64kBTU at 20 degree difference, with 6.5GPM. We have a TACO 007-F5 circulator for reference.

A second opinion from another vendor said that we should assume our circulator is at 4GPM and thus we only have 40K BTU delivered.



Recall that our heat loss is around 65kBTU.

Can you help resolve this discrepency?

CMadatMe

Not on A

Standard 20 degree delta-t at a velocity of 4ft per second. You need 1" pipe unless you plan on using a 30 degree Delta. If that is the case then a 008-VDT would be the way to go with the pump. You would then have control of the delta.



What velocity is that chart you are looking at showing. At how many feet per second? Your deliver gpm supplied by the circulator is dependent on the head it is overcoming. We never assume anything.



Example. You longest run from the outlet side of the circ through the zone back to the inlet side of the circ is 150 feet. If we use the basic forumla for head then we would have

9' of head. At 9' of head a 007 can move about 5gpm. If that run happens to be 100' then you would have 6' of head. Now that 007 can move 12gpm. The head in these cases is based on a velocity of 4ft per second.

lchmb

never assume

measure it out and do the calculation's.