Condensing Boiler Return Water Temp Too High

SWEI

Just let the boiler manage the circulator speed directly and this all gets better.

Paul48

Until Knuckleheads-R-Us put it on a system with a heatloss of 60k and radiation of 60k at 180*. Square peg, round hole.

Gordy

SWEI said:

Just let the boiler manage the circulator speed directly and this all gets better.

Steve ya listening? Your the only circ rep that frequents here. And thank you for that.

Paul48

The boiler manufacturers have to get on board. They have the 0-10v circs. Steve has posted the links before.

SWEI

Find me a 0-10V ECM circ sized for fire-tube boilers with firing rates lower than 399k.

Rich_49

As we tell everyone all the time ! Read the manual , page 31 .

http://www.htproducts.com/literature/lp-542.pdf

Paul48

7. VERY IMPORTANT – Minimum flow rates outlined in this manual must be maintained through the heat exchanger to minimize short cycling

The bottom of the chart being at 1 gpm means that is the minimum flow rate?

Rich_49

D. CIRCULATOR SIZING
The heat exchanger has a pressure drop that must be considered in your system design. Refer to Table 15for pressure drop through
the heat exchanger


There it is , Black and white . Feel free to call HTP to confirm . Don't take my word for it . Sounds pretty simple to me . Here is your true modulating condensing boiler , You asked for it and we listened is what I hear .

Flow rates actually coincide with modulation , no tricks , no gimmicks , no fuzzy math, no balancing devices , no buffers required , no primary secondary required . Just a flame that matches what the system needs as long as it's not below 1 gpm . Geez , imagine being in condensing mode with 150* AWT at cast iron rads at a 40 * Delta and not short cycling ?

Rich_49

@Paul48 . I remember a discussion I believe you initiated several months ago about Delta T circs and boiler side piping . Go ahead my friend just drop the P/S , you only need one pump . I guess you were onto something .

Paul48

I'm not doubting that's what it says. I just wanted clarification. You deal with the company, all the time. I can only say, I don't think it will be as clear to someone reading the manual for the first time. Especially because their other chart with design DT's through the HX are well above the 1 gpm. I seem to remember something about a 40*DT on high fire being used to determine minimum flow? Not arguing....just sayin'

I'm impressed with the unit, but I think they could do a better job of conveying what it is capable of....that's all.

Rich_49

I am quite happy with 1 gpm and will size my circs to achieve that at whatever Delta t . The penalties now are much better . Watch you head and flow don't try to lessen your head to the point that the VS circ will deliver less than 1 gpm . It is what it is and it is better than anything we have had . Just remember , system side flow on P/S must be greater than boiler loop .

ratio

Unless I'm mistaken, it is a silver bullet, the UFT can be essentially ignored during the engineering process, treated as a black box that just Does The Right Thing. Size your emitters right, let the ODR manage the water temp, leave the pump & burner on for the season. One start per year.

If it delivers.

SWEI

I've yet to see a mod/con with a flow sensor in it (thank God) and the math doesn't lie. They alarm on excessive ΔT, usually in two stages. Keep the flow rate appropriate to the firing rate and they don't alarm. The tricky part is tracking the up/down modulation of the boiler with the pump. I've yet to perfect that unless we are externally controlling both the firing rate and the pump speed.

Gordy

So your piped direct to the uft and your load takes you at 1gpm what now happens with system flow rates being less than 2-4 fps. Keeping air entrained, and air removal. That could be an issue unless zoning with loads. Some systems are not zoned. And 8 k still is not low enough for some of the excessive zoning seen. So now you go to p/s so you can keep the system flow rates higher.

Zman

I started another thread...

Rich_49

What's it called Carl ?

Zman

That would help.
http://forum.heatinghelp.com/discussion/156068/htp-uft-boiler#latest

Eastman

@ahovel

"Sounds like the two options are:
1. Change to one zone.
2. Change to a deltaT circulator.

Question.
1. Is there a way for me to perform the heat loss calculations?
2. Of course I'm attracted to what ever is the least expensive. So what would be entailed in changing to one zone?"

A few comments on your last post:

Regarding diy heatloss:
There are quite a few online tools to guide a homeowner through the process. I don't know what's popular or most accurate. Perhaps somebody will chime in with a recommendation. Try googling the subject in the meantime.

Regarding converting to a single zone:
A heat loss study will indicate what demands are required of the heating system in each area of the home. Perhaps some more baseboard is required in one place while less is required in another. Some balancing controls may need installation. Pipes may need to be moved or reconfigured etc..

If a single zone dominates the heat loss of the home, perhaps a single thermostat could be located in this area with complete control of the operation of the boiler. Thermostatic regulating valves could be utilized on the baseboard in the minor zones to prevent possible overheating in those associated areas. Note: A traditional TRV is capable of preventing overheating but is not capable of calling for heat. This approach prevents un-syncronized calls for heat from multiple independent thermostats without completely abandoning some of the desirable characteristics of independent zoning.

You could also investigate the possibility of zone synchronizing thermostats. Tekmar and Honeywell make systems that synchronize heat calls from independent thermostats. For example, Tekmar thermostats will coordinate the start times of all calls for heat. Zones that have less demand will shutoff their associated zone valves or pumps earlier in the heating cycle. In this way, all calls for heat overlap to the fullest extent possible. This preserves zone independence while minimizing the consequences of micro loading.

On another subject: JohnNY suggested the boiler may have some parameters that would allow the owner to modify the behavior of the burner. I believe you can cap the burner modulation output of this boiler during central heating calls and this may improve the overall efficiency of the system. I encourage you to review the install manual if you are interested in adjustments of this nature. Perhaps someone with direct experience with Rinnais will provide the forum with a detailed explanation of each parameter, as I found the documentation to be quite poor.

4Johnpipe

@ratio We have your exact described system in service just weeks ago...

ahovel

Thanks for all the responses.  So it sounds like the consensus is that there isn't much that can be done with the current system to get into condesing temps based on boiler design with the internal pump and the low loss header. So moving on from that.....

I did the heat loss calculation with SlantFin's iPad app.  Total heat loss for the house is 25,000 btu/hour on design day.  So the boiler is hugely over sized for sure.  Floor 1 is 13,000 btu/hour and floor 2 is 12,000 btu/hour for 70 degrees inside and 5 degrees outside.  I have a total of 42 feet of 1 inch baseboard on floor 1 and 73 feet of 1 inch baseboard on the floor 2.  

Based on the those numbers and boiler model, any reccomendations on boiler settings to get the best efficiency outside of condensing mode?

Gordy

First dial in the outdoor reset are you at 1.5 to start with?

ahovel

Are you refering to the K value? If so, that is set at 2.3 which is parameter 5. The outdoor reset (parameter 2) is set to 00 which is what Rinnai reccomends for baseboards. I'm getting my information from the attached PDF. Do you think I could go with less of a K value?

One of the parameters, parameter 49, is "Maximum pump capacity heating" the range for the setting is 40 to 100%. Currently it is set at 100. I wonder if I set this back to say 40%, if it will help with the return water temp etc?

ahovel

Sorry here is the pdf mentioned in the previous post.

Eastman

I read the install manual. I can't open the specific level II training document that ahovel posted on my computer though.

The Q series is marketed as having a fully modulating pump.

The E series is marketed as having an integrated single speed pump.

I hope I'm wrong, but the pump capacity parameter probably doesn't do anything for the E series. That is why I didn't mention it earlier. There's some other parameters that looked promising though.

Eastman

?? He said he has an E series.

Eastman

Well.. I suppose my reply still seems somewhat consistent with the discussion.

Gordy

Mentioned a k of 1.5 like hat a shot in the dark you can always go up or down. 1.5 gives lower water temps. I have a feeling you may be at 1.5 now. You are probably over radiated but a picture, and or brand of base board will allow us to determine its output ratings at different water temps.

Bottom line is you can only do so much with a boiler 4 times the heat loss, and when you zone things tank even more. A delta t circ is probably not going to get you much but will most certainly help since you are over pumping. The 73' baseboard may see excessive temp drop if your flow rate gets to low all though it is 1".