Under-radiated building

Dr. Z

Seeking opinions on a fix for a slightly suboptimal situation.
I recently had a Triangle Tube Prestige 110 installed in a 4-unit apartment building. Since the cold weather hit, I find that the heating demand for the two lower apartments is never satisfied (I've verified the thermostats are set at 72F/thereabouts).
My tech has confirmed that the ODR is set at maximum (this gives 150F water temp on a 20F day), and all is working well; however, the return water does not show a high temperature drop.
We've concluded that the problem is that the building does not have sufficient baseboard capacity. My tech proposes installing an in-line resistor with the ODR thermocouple to 'fool' the system into thinking the ODT is 10 degrees lower. This will boost the water temperatures by 10 - 12 degrees and deliver the needed heat to the apartments, and will still keep us within the upper water temp limit of 196F specified by the manufacturer.
Does this make sense? Anything else we should consider trying? Is there an easy/inexpensive fix for the baseboard issue?

J.C.A._3

You, or the tennants.....

Might try cleaning the baseboard elements before doing the drastic.

I've seen fins so packed with crap, that even 220° water wouldn't come close to the temp drop required. Dust bunnies, pet fur and dirt in general can do a number on the ability to transfer heat.

There's the cheapest way I can think of. Chris

Rob Blair

Maximum for TT Prestige?

Are you telling me there is a maximum setting for the ODR on a Prestige? I have never read the installation manual, but I find it hard to believe that you could not set a higher limit.

Rob

Uni R_2

Why not use the MCBA to do it?

Like JCA said, ensure that the current radiation is clean and not obstructed by furniture.

Attached is the stock ODR curve in blue as scenario #1. A bit steep but fairly reasonable curve for residences although not bad if never tuned. You buildings curve does not fit with the standard curve where only the boiler's max temp can be set and the maximum is 186°.

Someone will have to reprogram the ODR curves extended parameters on the installer's menu.

The cyan curve / scenario #2 shows what happens if you change your minimum temp [P5]. You'd have hotter water at warmer temps. Obviously, this is not what is happening to your building.

Your building's need for temps is increasing beyond the rate the boiler's calculated water temps. If the design temp is less extreme than the default 0°, then by changing the design temp [P6] to 12° for the sake of an example (copper coloured line - scenario #3).

I would guess that putting a 110 into a 4 plex wouldn't be the norm if your design temps were really low so this kind of change should resolve your issue.

Scenario 4 / magenta line shows how you could shift the curve [P5 and P6] so that at all temperatures are about 20° higher all the way along the curve, although again in this example, 186° happens at 12° OAT. So you hit the boiler's limit at a warmer outdoor temp.

What's the design temperature there? Being capped out a few degrees before design shouldn't be too big a deal unless there is setback and recovery being used.

Uni R_2

Rob...

It's a condensing boiler. It should only need 186° for DHW in normal well radiated buildings. That is the max... it has to vent through plastic.

joel_19

4plex

I would assume you put in the Prestige to lower heating cost. So the last thing you want to do is raise the water temp. Ditto the others about dirty baseboard. Then you can tighten up the building which will lower the water temp need and finally you could add more baseboard.

EX. We have a Vitodens in an electric conversion house with fairly minimal baseboard it ran no hotter than 136 supply over the weekend with temps in the teens that's what your after. Tricking the sensor defeats the whole purpose

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