question about the direc fired make up air unit
question about the direc fired make up air unit
(OP)
where can we use direc fired make up air unit? Somebody told me it is for any ventilation purpose as long as no one sleep in the conditioned area, such as restaurant and office. Direct fired unit makes me a little uneasy, is it really safe for people inside?





RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
We regularily use direct-fired in occupied spaces (not sleeping areas). The advantages are efficiency (~100%), turndown (30:1 as standard) and cost.
If energy is a concern, you can also arrange for a heat recovery system with the MUA. I have done plate, and heat pipe heat recovery with direct fired MUA.
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
The products of combustion of natural gas, burned in a high excess of combustion air, are CO2 and H20. What exactly is harmfull about that?
Dumping flue gas on people occurs when you don't make-up air that is being exhausted and chimneys from gas fired equipment start downdrafting from the negative in the building. I
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
I'm hesitant on direct fired equipment for occupied spaces simply because people are sue happy.
snip
Not to mention the carbon monoxide........
Not to mention the moisture problems.......
Not to mention the increase in carbon dioxide.....
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
What I would like to know is why the misinformation about the product? There are many applications when direct fired make-up air products are both acceptable, economical and safe.
Is there some history in the US of these things blowing up or causing huge IAQ problems?
From a safety point of view direct fired burners are always burning in a large excess of combustion air - meaning if you've selected the unit properly the only products of combustion are CO2 and H20. With an indirect burner the burner burns with very little excess air - meaning that if the HX leaks the products that escape into the airstream are much more dangerous, in fact the only time I've seen a piece of gas-fired equipment dumping high levels of CO into a space was an indirect MUA.
If anyone has seen a bad installation, or has heard of a bad experience please post.
RE: question about the direc fired make up air unit
RE: question about the direc fired make up air unit
The only caveat to that is what I've stated above and on another thread - they cannot be used in a flammable environment. Residential/Commercial applications are not a good choice either, because they simply don't have precision control.
RE: question about the direc fired make up air unit
The units for my designs go into food processing plants in which there can be no recirculation for one reason or another.
For what it is worth, my firm has just finished a design for a building that included about 400,000 CFM in 15 direct fired make-up air units heating for ventilation and clean-up operations.
RE: question about the direc fired make up air unit
Direst units in the UK ARE used, but I would say that discharging the products of combustion into a habitable space is not ideal. You would need a large quantity of fresh air to prevent or reduce condensation (if you are in a cold climate).
I personally use indirect to reduce any risk (however small) of CO poisoning.
Friar Tuck of Sherwood