TREAT FAQ: Heating and Cooling

Back to FAQ Page

What is the "Heating Month HDD/month?

The Heating Month Threshold (HDD/month) is used to identify the bills that do not have significant heating usage and are candidates for baseload estimation. The heating threshold is used for all analysis periods. TREAT uses the reference temperature and average daily temperatures to calculate heating degree-days in each utility bill. It compares the HDD value to the entered winter bill threshold. If the difference for a 30-day bill is less then the threshold, the bill is assumed to be a non-heating bill. This algorithm is applied to all the bills that have base and/ or cooling load in addition to the heating load. Heating threshold depends on the building heat loss rate, reference temperature, and specifics of heating system control. For example, you anticipate that the building has the heat loss rate (slope) of 15Btu/SF-HDD and you set your Heating Month Threshold to 50 HDD/month. Then all the months during which the heating energy usage was less than 15* 50= 750Btu/ SF-month will be used to calculate the base load. This input will work out well for the buildings where the heating system is turned off during warm months. Similar logic applies to cooling threshold.

Unfortunately, breaking the space into a cooled space and an uncooled space is not very plausible because when working with a large, multifamily building (188 units and 181407 square feet), and while knowing how many air conditioners there are, we do not know what rooms or what square footage they cool. From this lack of data, we feel that the number of assumptions we would have to make in order to create a second space would make our final results so unreliable that they would not justify the effort put in to come up with these approximations. The quality of modeling outputs is never better than the quality of modeling inputs. The best approach would be to survey the building and record in which rooms the AC units are installed.

If we estimate that 25% of the space is cooled, for example, and then set the unoccupied hours to 4 (which is 25% of the 16 hours we think the building is actually unoccupied), would that compensate for the discrepancy in the space cooled versus the entire space? You could use the same assumption (25% of space is cooled) to create a separate cooled space. Then assign walls, windows, appliances, lights, etc. to this space in the same proportion.    Return to Top

How much do we need for TREAT to be able to calculate a base load for a space that is both heated and cooled?

Generally in order to calculate base load TREAT needs at least one actual bill during which there was no cooling or heating (if electric heat). Heating and cooling usage for a billing period is determined based on average daily temperature for the time of the bill from a Daily Weather Data Library and heating/cooling threshold entered on General Billing Data and Analysis Periods screen. See User Manual, General Billing Data section for more details on the threshold.    Return to Top

Does TREAT require an AFUE or Steady State Efficiency?( Under Heating /Cooling)

Typically equipment efficiencies are stated in terms of AFUE (annual fuel utilization efficiency). This number is usually less than the steady state output, significantly less for older equipment. Sometimes this is very different, such as older equipment that might have a steady state efficiency of 80% and a AFUE of 60-70%. The efficiency is used when we convert heating load to units of fuel or $ used for heating. In this regard seasonal efficiency makes most sense. For larger systems AFUE is not available and must be estimated based upon steady state efficiency.    Return to Top

Under Heating / Cooling - Is the efficiency an AFUE value or the Steady State Efficiency?

The efficiency one should enter in TREAT is the AFUE (a number which can only be guessed at for large steam boilers).

Generally, the primary goal of your modeling is to calculate annual energy usage in the building. You verify it against billing, calibrate the model and predict annual savings from recommended improvement packages. For this purpose AFUE makes more sense then steady state efficiency, which may be significantly higher than AFUE, especially for older systems. If you use steady state efficiency you may underestimate annual energy usage and annual savings from improvements.    Return to Top

If we just put the cooling thermostat on to the existing thermostat, doesn't the program assume that the air conditioners are trying to cool the whole space?

Yes it does. Not all of the apartments have air conditioners. In order to model the building accurately you need to split it into two spaces. One space that includes all air-conditioned areas, and another space without air conditioning. The same rule applies to modeling mechanical ventilation, overheated areas or areas with different indoor temperatures/schedules.    Return to Top

I dont know what should be my heating month threshold and cooling month threshold. I would put 50 and 55 as the value for both the fields? What is recommended.?

The Heating Month Threshold HDD/month is used to identify the bills that do not have significant heating usage and are candidates for base load estimation. TREAT uses the reference temperature and average daily temperatures to calculate heating degree-days in each utility bill. It compares the HDD value to the entered winter bill threshold. If the difference for a 30-day bill is less then the threshold, the bill is assumed to be a non-heating bill. This algorithm is applied to all the bills that have base and/or cooling load in addition to the heating load. Heating threshold depends on the building heat loss rate, reference temperature, and specifics of heating system control. Example: You anticipate that the building has the heat loss rate (slope) of 15Btu/SF-HDD and you set your Heating Month Threshold to 50 HDD/month. Then all the months during which the heating energy usage was less than 15* 50= 750Btu/SF-month will be used to calculate the base load. This input will work out well for the buildings where the heating system is turned off during warm months. Cooling Month Threshold HDD/month is used to identify the bills that do not include cooling. The procedure is similar to the one described for the winter threshold. This algorithm is applied to all the bills that have a base and/or heating load in addition to the cooling load.    Return to Top

From the modeling point of view does it matter if there are the same thermostat controls for both heating and cooling or if there are two different thermostats?

You should use the thermostat to define cooling setpoint and hours of usage.    Return to Top