HEATING CASE STUDY

Contents

1. Introduction

2. Objectives

3. Model

4. Simulation

      4.1. Heating requirement without heating control  for 2 kW heaters

      4.2. Heating requirement with heating control  for 2 kW heaters

      4.3. Use of 1.5 kW heaters with temperature control

5. Results Summary

6. Conclusion

·         2 * 2kW convection heater

·         5 * 36W fluorescent lamps

·         2 occupants

·         2 computer and 1printer

·         Infiltration when doors open: 3 ac/h

·         Infiltration when doors closed: 1.5 ac/h

  Back to Top

The following assumptions were made:

• heating behaviour of occupants:

  • 7:00 – 8:00 both heaters on max. power (2 x 2000W)

  • 8:00 – 12:00 both heaters on middle power ( 2 x 1250W)

  • 12:00 – 18:00 both heaters on low power (2 x 750W)

The graphs below show the ambient temperature, dry resultant temperature inside the cabin and the heating load for a typical winter week.

The upper continuous line indicates the dry resultant temperature inside the cabin, the discontinuous line shows the heating load and the lower black line the external temperature .

Heating energy: 115 kWh

Heating hours: 57.5 h

Carrying out an analysis of the current situation it is estimated that without automatic temperature control the annual heating demand is about 3000kWh per cabin

Typical winter day

Back to Top

The heating control is set to 22°C air temperature in order to maintain a dry resultant temperature of 20°C inside the cabin.

The graphs below shows the ambient temperature, dry resultant temperature inside the cabin and the heating load for a typical winter day considering the starting time for heating equal to the start of occupancy.

The upper continuous line indicates the dry resultant temperature inside the cabin, the discontinuous line shows the heating load and the lower black line the external temperature .

Heating energy: 14.6 kWh

Heating hours: 11.5 h

Setting the heating control to 22°C, the required dry resultant temperature (20°C) can be maintained from 9am on until the end of the working day. Thus, an optimum starting time for the heating has to be identified in order to provide the required thermal comfort from 7am on. In the pictures below the upper line shows the dry resultant temperature, the middle the heating load and the lower one the ambient temperature . The picture on the left shows a typical winter day.

Typical winter day

Define optimum starting time for heating

By running a number of simulations, we have identified the optimum starting time of 6am. For the starting time set to 6am the heating energy delivered and dry bulb temperature of the cabin are shown in the figures below for a typical winter day as well as for an exceptional cold winter day.

In both cases the optimum office temperature is reached when the offices are starting to be occupied.

The upper continuous line in both graphs indicates the dry resultant temperature inside the cabin, the discontinuous line shows the heating load and the lower black line the external temperature.

Typical winter day

Exceptional cold winter day

Considering a heating season from October to March, using a heating control system with an optimal starting time of 6am, the annual heating demand is 1758kWh

The optimal use of a heating control system requires that the door is closed most of the time in order to reduce the heat loss through infiltration. This would further reduce the annual heating demand down to 1055 kWh.

However, having the door closed most of the time, the carbon level in the cabin is likely to exceed its maximum level. Please refer to the ventilation requirements for various areas assessed in the Ventilation section of this project. For a cabin this size used as office containing 2 occupants, 1.5 ac/h are sufficient to meet the required ventilation and thus provide enough fresh air inside the cabin.

The table below states the percentage energy savings for both cases.

It is therefore estimated that applying heating control can reduce the heating demand about 50% in average.

Back to Top 

In this part of this case study we are going to evaluate if the use of 1.5kW (instead of conventionally used 2kW) electrical heaters would satisfy the heating demand inside a well insulated cabin. We will do this by assessing if using 2 x 1.5kW heater is adequate to maintain a dry resultant temperature of 20°C in the model cabin during a cold winter day when:

       a)       the cabin is occupied by 2 person and contains 2 computer and a printer.

       b)       the cabin is occupied only by one person.

The optimum starting time is set to 6am as identified before. 

The results are demonstrated in the following

      a)       cabin occupied by 2 person and containing 2 computer and a printer

Doors mostly open

Use of self-closing doors

       b)      cabin occupied only by one person

The use of 2 x 1.5kW heaters is sufficient to maintain a dry resultant temperature of 20°C. The pictures below show the maintenance of the required dry resultant temperature on a cold winter day for the two cases:

• Doors mostly open (3 air changes per hour)
• Use of self-closing doors (1.5 air changes per hour)

The upper continuous line in both graphs indicates the dry resultant temperature inside the cabin, the discontinuous line shows the heating load and the lower black line the external temperature.

Doors mostly open

Use of self-closing doors

It is therefore shown that 1.5kW heaters can replace the 2kW convectional heaters. Using 2 x 1.5 kW heaters in a well insulated cabin can satisfyingly maintain a certain comfort level even in extreme cases e.g. a cabin with little casual gains on a cold winter day.

For a heating season from October to March, using 1.5kW heaters and a heating control system with an optimal starting time of 6am, the heating demand is 1750kWh when the doors of the cabin are mostly open and 1045kWh when self-closing doors are used.

Back to Top

All values gained from the ESP-r simulation are tabulated below

The table above is based on the following assumptions:

• Setting the heating control to 22°C, a the required dry resultant temperature (20°C)

• Considering the office operating time between 07:00 – 18:00

• Start of heating system (with temperature control) at 6:00 am

• The cabin is occupied by 2 people and contains 2 computers and a printer

• Consider the air change rate of 1.5 with doors closed condition and an air change rate of 3 with the doors open condition.

 Back to Top

As result of our case study we can say that using a heating control system energy savings up to 41% can be obtained with doors open and up to 65% with doors mostly closed. Hence on an average the energy consumption for heating inside a cabin can be reduced by 50% when using a heating control system. Furthermore, it is shown that for well insulated cabins current heaters with a capacity of 2kW are oversized. The use of 1.5kW is sufficient and would therefore reduce the cost for heater fittings for new cabins as well as reduce the material usage of a cabin since these heaters are smaller than the conventional once.

Thus, replacing the current heating system with new automatic temperature control heating system of reduced capacity would result in maintaining the required temperature with little more running time when compared to the 2 kW temperature control system, but giving more consistent load to the generator and reducing the investment cost of the heater too.

Back to Top