hydro-air efficiency

tom_49

Hi guys,
What do you think that actual AFUE of a hydro-air system is? What I mean is, you take water, heat it up at say 84% eff. on the boiler. Now you've got to send it down pipes to get to an air handler, pump it through a coil, now turn on the blower, blow the heated air down cold ducts to get to the end user. That heat sure goes through alot before it puts 1 btu into the space. Any thoughts? Thanks Tom

RoosterBoy

I just got a buderus g115 and air handler and I hate that my boiler has to go on 2 times in one heating cycle and the second time it goes on it only goes on for 1 to 2 mins

so what I think I have to do is throw a aqustat on the airhandler so it turns the fan on at 130deg and shuts the burner off when it hits 180 but dose not turn back on the burner till the water gets back to 130deg

I am using the 2109 controller now and the burner heats the water up to 180 but then turns it back on when the water go's to like 165 170 and turns burner on for 1 min or so I hate that so I hope a aquastat will fix it

at least with my old forced air furnace it would stay on till the t-stat was happy and not come on twice

like at night im sure with a boiler if I heat my house during the day at 72 and at night I want to drop it down to 65 to save oil in the morning im sure your boiler would have to come on 2 or 3 times just to heat your house back up to 72 with my old furnace id have a nice long burn with my burner I am thinking if I switch my whole house to baseboard that it wont be like that and I can keep the house at 68 and it will feel like 72

thanks

Ron Schroeder_2

Hi Roosterboy,

What size G115 do you have? What is the BTU capacity of your air handler? If it has multiple speeds, what speed are you running it at?

Ron

RoosterBoy

I asked my HVAC contractor to take out all my old duct work and put in one big truck down the middle of my basement and put a return beside it also on the other end of the house instead of duct I am having him put in baseboard.

he installed a buderus g115 model 28 with r2109 and lt160 hotwater tank with a 2 ton air handler the speed is on high

right now I keep my t-stat at 72 and it turns on a 72 3/4
just so my t-stat satisfy quicker but I keep the fan on all day so when the burner turns off and by the time my boiler temp goes down to 130 my t-stat is at 74

but I hate having the fan on all day so I am putting in new duct maybe that will give me more cfm's and will heat my house faster

any advice you can give me to help me with my new system would be great my HVAC contractor is so busy but he is giving me a price today for new duct work and if I ok it he will start tomorrow so im going to ok it I have no choice im not happy with it so far I think

I think the 2 problems I have is

1) duct work is to big for my 2 ton air handler I get very low cfm's

2) no aquastat on the airhandler

so im going to talk with him tomorrow

thanks

Ron Schroeder_2

Hi RoosterBoy,

The air handler is definately small for your boiler. The G115/28 has a net IBR output of 85,000BTU but 2 tons is only 24,000BTU. Most air handlers have a heating output larger than their cooling output but I doubt it if it is over 40,000BTU. That air handler simply can't use all of the heat that the boiler is producing. If you can increase the differential on the upper limit, it might help the situation some what.

Without a heat loss for your house, I can't tell you if the boiler is over sized too.


Ron

Mitch_4

Air handler

2 tons is for A/C. Check the specs on your airhandler. I have a lifebreath unit the does 2.5 tons, and is rated for 90,000 btu's in heating mode.

low CFM is semi-irrelevent it is how many BTU/CF you deliver, and how the system is balanced.

From what I read, by running the blower 24/7, you are pushing cold air across your heat coil. this will pick up the heat from the boiler water. unless you have something to stop it. as you cool the water in the coil in the AH, it wil induce circulation in th eboiler and more hot water will enter the coil. (some call this Ghoist flow)

So even though your stat is not calling, you are putting heat into the space, hence the overshoot to 74°

Check the specs on the air handler regarding air flow requirements for the coil, fan capacity, and required delta t across the hydronics coil @ you r boilers temp.

The idea that a 2 ton air handler will not handle 85,000 btu of heating is ridiculous. It like saying that a 100,000 btu furnace should do 8+ tons of cooling. I t ain't gonna happen.

Good luck.

Mitch

Ron Schroeder_2

Hi Mitch,

I got the 40,000BTU from the three air handler data sheets that I had lying around. It's quite possable some brands have even higher heating outputs. But you do have to flow more CFMs to get more BTUs for a given water temperature, just like you have to flow more GPMs with hydronic heat.

Speaking of that, you do need a properly sized circ for the air handler too.

Roosterboy......what is the make and model of your air handler and the circ?

Ron
Ron

Ron Schroeder_2

Tom,

In general, Hydro air is as efficient or more efficient than a furnace. The boiler might be a percent or two higher in efficiency and the loss from the hot water pipes is usually less than the differance in efficiency. Hydro air also allows easier zoning with multiple air handlers. Of course poor design, sizing and controls can make either perform poorly.

Ron

RoosterBoy

I have a freedom air made for ipc it's a 2ton and I am using a taco 007 copper goes 27 feet supply and 27 feet back return

I am thinking guys to just hell with the air and have them put it baseboard in the whole house.

hay run when you get up in the morning how many times dose your boiler cycle to bring your house up to heat

im assuming you have baseboard heat and heat with oil

and is it true with baseboard that I can keep my house at 68 and it will feel like 72

let me get you the model number to my air handler maybe you can tell me how many btu's of heat it should pump out

it's Freedom Air MFG for IPC MODEL# AHXW2400A1 that's 2
zero's

thanks

Mitch_4

I apologize if I insulted / offended

I am not doubting your figures, but it'll vary based on fan design, not btu capacity is all I was trying to say.

Ron Schroeder_2

So far I have not found a web site for Freedom Air MFG. Where are they located? Do you have a phone number?

Ron

Ron Schroeder_2

Hi Mitch,

No insult taken. It's sometimes hard to remotly diag. something without specific data sheets.

Ron

Mitch_4

I punched the numbers/ name and

varuiations there of to the unit info into google, and it came up blank except IPC manufacturing, and they make wireless LAN equipment.

Can you verify who made it?

Mitch_4

I'm Glad

you weren't insulted. Sometimes the writtren word comes across the wrong way. This is a great forum, and I like the exchange of ideas...not insults.

Ron Schroeder_2

Hi Roosterboy,

Is the copper at least 1" and preferably 1 1/4"? At 20 degree delta T you would need 8.5GPM for 85,000BTU which is .5GPM over the reccomended flow for 1" copper at 4 feet per second. Don't worry about the extra .5GPM, it's not really important in the real world but if the copper is 3/4", you're really pushing it.

Ron

RoosterBoy

it's 3/4 copper that's going from the taco 007 to the air handler I talked with him today he give me his price to do all new duct work and he will put baseboard on the other half of the house I will make that it's own zone

so are you saying that 3/4 inch is to small my heat load for the whole house is 50,000btu the air handler side will need 30,000btu and the baseboard side will need 20,000btu

I also had him install with the boiler a 42gal buderus lt160 indirect hotwater

let me know what you think. should I have him install baseboard in the whole house I asked him today and he said he did not want to see me waste all that money I spent on the air handler if we are not going to use it now he wants to make it work and thinks that if I have him install new duct it will work much better

thanks

Ron Schroeder_2

> it's 3/4 copper that's going from the taco 007 to

> the air handler I talked with him today he give

> me his price to do all new duct work and he will

> put baseboard on the other half of the house I

> will make that it's own zone

>

> so are you saying

> that 3/4 inch is to small my heat load for the

> whole house is 50,000btu the air handler side

> will need 30,000btu and the baseboard side will

> need 20,000btu


3/4" is too small to take 85,000BTU out of your boiler but might not be too small for your air handler. This is just rough without a datasheet on the air handler but 3/4" will handle 40,000 BTU at 20 degree delta T.

>

> I also had him install with the

> boiler a 42gal buderus lt160 indirect

> hotwater

>


I have the same indirect on my own system and on customers. I like it. An inside out indirect might have been a better choice for you because it could also serve as a buffer tank.

> let me know what you think. should I

> have him install baseboard in the whole house I

> asked him today and he said he did not want to

> see me waste all that money I spent on the air

> handler if we are not going to use it now he

> wants to make it work and thinks that if I have

> him install new duct it will work much

> better

>

> thanks


Do you have the origional duct work from when you had a furnace or do you have new duct work too? What was the BTU rating of the old furnace?

You have a number of options at this point. Don't rush in to anything.

Ron

RoosterBoy

oh hi Ron coming out of the boiler my supply and return header is 1/12 inch black pipe or 1/14 but it is black iron

my old furnace was a 85,000 btu and it heated the whole house with the duct work I have but this 2 ton blower weel is set to high and I don't get enough cfm out of it to heat the whole house.

if you had this problem what would you have done. baseboard or new duct with half the house baseboard?

thanks

Ron Schroeder_2

Hi Roosterboy,

If the house heating load at design temperature truly is 50,000 BTU then I would probably use a G115/21 boiler unless there was an abnormally high DHW usage. Since I prefer baseboard heat, that is what I would have gone with. Personally, I would have central air but I would be carefull to not over size so I would get good de-humidification. I would analyse the ducts to make sure they were suitable for the A/C capacity. If they were over sized, I would look to see if reducing the size of the registers would solve the problem without replacing the ducts. I would make sure the ducts were well sealed and that any ductwork in unconditioned space was well insulated. I probably would use a water coil in the air handler for suplimental heat but not primary heat.

I would use an inside out indirect with a anti-scald thermostatic valve on the output for both DHW and as a buffer tank to prevent short cycling. I would use a control with at least adjustable differential on both the low limit and the high limit. Of course this is based on past experience, personal preferances and guesses as to what your house is like.

Ron

tom_49

> Tom,

>

> In general, Hydro air is as efficient or

> more efficient than a furnace. The boiler might

> be a percent or two higher in efficiency and the

> loss from the hot water pipes is usually less

> than the differance in efficiency. Hydro air

> also allows easier zoning with multiple air

> handlers. Of course poor design, sizing and

> controls can make either perform poorly.

>

> Ron



Hi Ron,
I install lots of hydro-air units, they're great. I like there flexibility . We use multi-zones, DHW, BB in finished basement, and best of all 1 heat source ( and venting ). I just question the overall " system efficiency". I mean if I install a 92% gas FHA furnace, pretty much all of the btus produced get into the space. Whereas w/ hydro-air, you have to heat alot of pipes & ducts to get the heat to the space.

Dont get me wrong, these systems are great from my point of view. But the overall A.F.U.E of the "system" I question.

DaveGateway

First check

the 2109. The boiler should not be cycling on again at 165°. By keeping the fan on, once the thermostat is satisfied, the coil is still hot and you overshoot the temp to the house. An aquastat should be only needed to turn the fan on once the boiler water gets to over 130° so you don't get a blast of cold air. You might want to look at only allowing the boiler to go to 180° when the indirect calls for heat. The 2109 should have outdoor reset and probably could keep the boiler between 120 and 160 for the hydro-coil, varying the water temp based on outdoor temps.

Ron Schroeder_2

Hi Tom,

You can't "lose" BTUs. You can only put them somewhere you don't want them. It all depends on where you run the pipes and a few other minor things assuming the ductwork is the same. It will usually be very close unless you use an indirect on the boiler. With an Indirect on the boiler (which you can't do on a furnace) the boiler wins. A boiler will have more BTUs in itself than a furnace due to greater thermal mass but even they can be put to use with post purge running of the circulators.

Ron

tom_49

Ron, I guess my question is answered. Thanks. I guess the notion of losing btus doesnt make sense, unless of course its up the flue. I agree w/ the boiler winning thing.

I find myself doing more and more hydro-air jobs, and I gotta tell ya, I love the idea of 1 heat source and vent. Im just trying to have some more answers for my educated(?) customers. Thanks Tom

Mike T., Swampeast MO

Air is Air

As with any forced air system, the ductwork has much to do with total system efficiency. Leaky, un- or poorly-insulated ductwork running through unconditioned spaces results in inefficient delivery/removal of BTUs regardless of the nature of the appliance producing the heat.

Poor balance between return and supply air will still result in some spaces "sucking" outside air with others "blowing" conditioned air.

If the air system is being used for both heating and cooling you still have to make a comfort concession somewhere and return design becomes ever more critical due to the fact that A/C returns MUST be oversized relative to heating returns.

Ron Schroeder_2

I don't think the 2109 has outdoor reset. I think that the 2107 does. I'm hoping that Joe@Budurus will jump in here about the fine points of the controls.

Ron

RoosterBoy

hay Ron thanks for all your help. your right the 2109 dose not have a outdoor reset and im kicking myself in the you know what for not getting the 2107. but my guy will be out here today and he said he is with me till the end on this and that he will get everything working the way I like

so I have to make my mind up as to what to install he gave me prices so it's up to me now. and im stuck :-)

I did not foresee all this expense I thought this boiler setup with hotwater was going to work the same if not better then my FHA furnace. im sure it will but boy am I paying for it now.

I could not do this without all your help and good advice
knowledge is the key and I hope I end up warm this year.

half of my house is unheated and the other side is working hard to keep me warm. I may have to burn wood for another week wile we get everything in I just want it to be over

thanks