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the end use of low radiant floor heating is too low in the os report

asked 2016-03-17 20:08:26 -0500

Hyphen32 gravatar image

updated 2016-03-17 20:47:56 -0500

Hi everyone,

I am doing a simulation for a radiant floor heating system. Now I am using a template found in BCL(by apply measure). The HVAC template I used named AEDG Office HVAC radiant DOAS. My building is a residential building with 6 stories plus 2 parking lots underground. There are 36 units in the building.

Now after the simulation, the report shows that heating only accounts for 10% for the total end use, while lighting and interior plug loads occupy 48% and 40% respectively. That does not make sense to me. My understanding is heating should be the largest part, around 50%~60% for the total energy consumption.

I tried to adjust the heating schedule. The original setpoint is 18 degree c for heating, I change to 40 C(I guess whenever T below 40C, the radiant heating system will start to work?) However I still get the same number, 10%. I also check the definition for lighting and internal equipment, there are like 4 W/sq meter. Therefore, I guess there is something wrong with the heating only. The number is too low. And when I read the natural gas consumption for heating, the peak shows in Jan and Dec, only 17 MBTU(which is 5kwh). 5kwh one month for the whole building thats ridiculous

Does anyone know how to fix it? Thanks for any help.

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answered 2016-03-28 15:09:18 -0500

Radiant systems in E+ are unusual in that the temperature set point isn't controlled by the thermostat (as you have noticed), but instead by schedules in the radiant objects themselves. You can also control what type of temperatures (Mean Air, Mean Radiant, Operative) the setpoint schedule represents using this field.

I suggest checking out these schedules, and then plotting the zone temperature (whichever type you set as the control type) vs. time to see if the setpoint is being met. If the temperature is way below setpoint, you've found your issue. If the temperature looks OK, I would start by isolating the loads (using Ideal Loads). If the loads look like what you expect using Ideal Loads, you'll know it's an HVAC problem. If the Ideal Loads look too low, check out the outdoor air, the infiltration, and the envelope performance.

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answered 2016-03-29 09:41:38 -0500

Firstly have you checked that your rooms are meeting their temperatures requirements, if not, I would make sure that your zone sizing and system sizing objects are showing the correct values for sizing the radiant slabs. Secondly, if your rooms are meeting setpoint there are a few things you might want to check with a quick hand calculation:

  1. envelope properties, is you envelop well insulated? if so the heating demand from the space is going to be lower than if there is very little insulation
  2. infiltration rates, do you have a lot of outside air coming into your space through infiltation, if so your heating demand will be higher than with a tight envelop
  3. lighting and plug load in the spaces, 4W/ft² seems quite a large load to me for a residential space, i would expect something closer to 2W/ft². You might want to check these and then check the schedules you have applied to them, are the lights and equipment on 24 hours a day, is this realistic
  4. how are you putting fresh air into the space (through the DOAS?) what temperature is this air entering the space and what is the flow rate, the higher the flow rate and temperature the less work the radiant slabs have to do.

My suggestion is to take all these numbers and for the heating design day (and/or for the average temperature each month) calculate what your heating demand is. Check this against the simulation and make sure all your inputs are what you would expect. Then if things still aren't working as expected, I would suggest reading the inputoutput guide, this will help you understand the objects you are using better.

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Asked: 2016-03-17 20:08:26 -0500

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Last updated: Mar 29 '16