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Re: [TRNSYS-users] Type700 question

Hello Nick,

So during the three days the temperature tank drops, the boiler is completely off, no? Then on the seventh day, the boiler has to bring the lower temperature tank back up to setpoint temperature?

Thinking about this, I do not think there would be much difference between the two scenarios unless there was a significant efficiency penalty for turning on and off the boiler. Essentially, it will be heating the same amount to temperature - whether that water has been "chillin" for three days and then the boiler has to bring all of that water up to setpoint temperature or whether the boiler consistently keeps the water at the setpoint temperature.

Alright, now that I am thinking about this too hard, we may have to do some simulations to test this. Nick, I would reccommend simply doing this on a smaller scale (1 or two weeks) with these two different scenarios to see what happens, how the systems ! respond, and the resulting energy consumption on that scale.


Best regards,

Matt Duffy




----- Original Message -----
From: "Nicholas LaHam" <ndlaham@gmail.com>
Sent: Mon, April 18, 2011 8:29
Subject: [TRNSYS-users] Type700 question

Hi all,

 

I have a question about Type 700, the boiler component, if someone has experience with it. I have a flow profile running into a tank, with a boiler loop circulating through it to meet the energy demand. Boiler is set to 1 million kJ/hr whi! ch is just enough to meet the temperature demand of the tank at its pe ak load.

 

Here is the problem:

 

I have my flow operating 4 days out of the week. At first I only had the boiler turning off when the temperature was met (controller with 2, -2 deadbands). When I looked at the required boiler energy input integrated over the course of the year, the number looked right, but I wanted to reduce it. In order to do this, I used another controller on a time delay to lock out the first controller the other 3 days of the week, so the boiler wasn't trying to heat the tank all weekend wasting useless energy.

 

What I noticed however was the required energy input barely changed. I know the new controller works properly, because I can now see the tank temperature dropping after the first 4 days and then not rising until a few hours before the start of the week.

 

I think the energy savings should be more significant. I'm only saving around 10 therms a year in  a 8500 gallon system. This is very small. The boiler should be saving that at least every day it is turned off.

 

Any ideas why the difference is so small?

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