BV² - Fördjupning
Further information
Increased need for energy calculations

As energy prices rises and a greater awareness of global environmental issues ensues, it becomes more important to optimize building energy use. Higher demands are being put on buildings with emphasis on energy efficiency. New rules in the BBR and the Law on Energy Certification, makes it necessary to estimate and record building energy use in a reliable way. With BV2 it is easy to compare the profitability, operating costs and energy use of various techniques and principles.

Nowadays, it is not enough just to design the building installations to meet the design conditions, such as the hottest or the coldest days. You should also be able to show what the proposed solutions will mean in terms of annual energy use.

BV2 is developed with the purpose of being the most practical calculation tool in use that can satisfy those needs.

BV2 has been made to operate easily in practical situations

It is structured in a way that makes most commands self explanatory and together with explanatory help you get guidance on possible ambiguities.

With its customizable input structure, BV2 is unique. In almost every part of the program, you can choose between a limited amount of input data or more extensive and detailed input. The last option is particularly useful in reconstruction or in the early stages of construction. The latter option is useful for example in the detail design phase. You get the calculations results on the screen in front of you. Each time a change is made in any building or technical system, you can immediately view the results.

The results are available in clear tables, bar charts or duration diagrams. With the help of BV2 you can easily calculate both design effects and annual energy needs allocated over heating, cooling and electrical systems.

No two buildings are alike! In BV2, you therefore have greater potential to choose between a variety of heat producers, from a wood burning boiler and a solar heater to a heat pump. It is equally easy to choose between different types of ventilation systems and controlling them, as it is to choose air- or waterborne comfort cooling or district cooling.

In practical situations you usually have to make several energy calculations on the same building in order to try different solutions. BV2 is particularly suited to study the consequences of different choices, such as:

  • What is most profitable, to install air-or waterborne comfort cooling?

  • What is the difference in cooling and heating if window A is chosen instead of Window B?

  • What happens to the indoor temperature if I rebuild/build onto my existing building and would like to keep the old cooling system?

  • Which type of climate control system will provide the lowest electricity consumption?

  • How does the building’s design and location impact the need for cooling and heating energy?

  •  Which heat production system provide the lowest life-cycle cost, a heat pump or a pellet boiler with solar?

A little about using sustainability graphs for energy and effect calculations

The calculation of the building heat balance in BV2 is based on the yearly outside temperatures. It separates days from nights. Below is a brief review of how the building Heat Balance in the Duration Chart (BV2) can be presented in a graphical form and how it should be interpreted based a sample of what can be viewed on the screen.

  • Red box corresponds to the building's requirements of thermal energy for heating
  • Blue box corresponds to cooling requirements for cooling
  • Purple box corresponds to the heat stored in the building structure between day and night.

Decisive (main) heating power requirements are found on the coldest winter night, while the design cooling power needs are found on the hottest summer day.

The building’s heating requirements

It is important to understand that the building's heating power requirement (red bar) refers only to the building’s requirement of the added thermal energy for heating in addition to the heat generated by people, lighting, appliances and solar radiation in the building. Its heat energy is sometimes called the heat deficit. The thermal energy need not be equal to the amount of purchased energy, which is influenced by the type of heat that the building has.

If the building has a boiler, the amount of purchased energy is larger due to losses in combustion in the boiler. If the building is connected to district heating, the amount of purchased heat is equal to the heat requirements as the heat loss is virtually negligible. If the building instead has a heat pump, and perhaps also in combination with a solar heating system, the amount of purchased energy is considerably smaller than the building’ s heating requirements.

In addition to the building’s need of energy for heating, heating energy is needed to heat the hot water system and the ventilation system. This heat quantity is not represented in the duration chart above. If the building is ventilated with exhaust air, the ventilation air is heated directly in the building's rooms. If the ventilation air is supplied via fan system, the air is heated separately in the air handling unit.

The building’s cooling requirements

During part of the year there is an excess of thermal energy in the building (blue bar), which leads to high indoor temperatures if the excess heat is not removed by means of a comfort cooling system. In everyday speech the surplus heat is called the building cooling requirement. The building cooling requirement is in most cases greater than the purchased energy to the comfort cooling system. How much the difference is between cooling requirement and the purchased energy for the comfort cooling system depends on the type of system the building is equipped with and how the comfort cooling system is designed and dimensioned. For example, the difference between cooling requirements and purchased energy for the building is affected by whether or not the building has air-borne or water-cooling systems, if there is a cooling machine or district heating and if any type of free cooling is used.

To learn more about BV2, please contact us


© CIT Energy Management AB
Datum: 2011-11-23