Buildings and industry Case studies
Published: 1/6/2018

Apartment house Myslíkova, Prague 2

Today, controlled ventilation is increasingly used not only in residential buildings, but also in commercial buildings. In larger buildings with controlled ventilation, which are shared by more tenants, the question arises as to how to fairly allocate the costs of air treatment and distribution by central air conditioning and zone controllers VAV or CAV.

The allocation of heating costs using ratio indicators (heating cost allocators, RTN) already has its history and the individual principles and algorithms have found their supporters and opponents, while the calculation of ventilation costs has so far been dealt with on a flat-rate basis. The swallows in this respect are the housing units in the Odborů 2 house, where a measurement and control system with proportional readings of energy consumption for apartment ventilation was installed. All the functions described below were added as additional blocks in the freely programmable Domat control system, so that the measurement and control system did not require any additional hardware or software components.

The building is equipped with a central air conditioning unit for 20 apartments, located on the 1st floor. This HVAC unit, but also another HVAC for non-residential premises, is supplied with heat and cold by a Bluebox MU ECOS A heat pump (DHW) with a maximum input of 8 kW, a maximum heating output of 30 kW and a maximum cooling output of 27 kW. In addition to a two-pipe heat exchanger for heating and cooling, the air handling unit is equipped with a continuously adjustable el. reheating and bypass recuperator. The fans are controlled by frequency converters (FM) according to the pressure in the duct to guarantee constant pressure conditions in the duct even with different numbers of ventilated apartments.

Each apartment has two independently controlled dampers: on the fresh air supply from the air conditioning and on the exhaust from the apartment (toilet, bathroom). The investor required two ventilation modes:

- air exchange, when both flaps are open and the balance is balance
- dextraction, when only the exhaust flap is open and the exhaust air is compensated by infiltration

The dampers are electrically operated by buttons located in each apartment. The button in the living space opens the inlet and the exhaust, the button in the bathroom only opens the exhaust flap. The basic heat demand in the apartments is covered by radiator heating with thermostatic heads. Air conditioning is used only for ventilation, it is not the task of solving the heat balance of apartments.

The consumption of the source part is measured by six energy meters:

  • Electricity meter for heat pump
  • Calorimeter for heat and cold HVAC apartments
  • Calorimeter for heat and cold air conditioning non-residential premises
  • Electricity meter for FM exhaust fan HVAC apartments
  • Electricity meter for FM supply fan of HVAC flats
  • Electricity meter for electric heating of HVAC flats

In order to make the consumption budgeting as objective as possible, the investor decided to summarize the immediate power consumption of the system and divide it by the number of currently active flats. The resulting power consumption per active apartment is integrated in time. This gives the relative energy per apartment. The total invoiced energy consumption (electricity for fans, reheating and heat pump) for ventilation of the apartment is divided according to relative energy. In fact, the billing algorithm will be a bit more complicated, part of the total consumption will be charged as a flat rate, similar to RTN, where according to RTN data only 60% of consumption is calculated, while the remaining 40% is divided according to heated floor area.

Because the heat pump can supply one or both HVAC units and we need to know the consumption only for HVAC apartments, we calculate the power consumption. energy for heat pumps in the ratio of power inputs flowing through calorimeters for HVAC apartments and HVAC non-residential premises. Additional costs are realized in the energy consumption for the supply fan, the circulation pump of the register and the electric reheating (which is measured separately). The sum of the power inputs of the heat pump part, the supply fan, the pump and the el. reheating is taken as the total input for supply and reheating or cooling of air for apartments.

This power input is divided by the number of open supply flaps. (If all dampers are closed, the air conditioning is switched off and the algorithm is not functional.) Power input per damper is integrated with a resolution of 1 s, ie every second a proportional part of the (instantaneous) power per damper is added to the accumulated variable. This variable contains the "clapperwaters" used for billing, not direct invoicing. The interval for storing the measured values ​​is 1 h. Since the dampers are two-position and with active ventilation the air flow should be constant, it is not necessary to consider the degree of opening of the damper, resp. amount of air supplied. This would be a topic in VAV systems and the algorithm would have to be slightly modified.

In principle, the same applies to the exhaust, only the power of the exhaust fan is taken as the instantaneous power input. We therefore assume that an open exhaust flap in an apartment where there is only exhaust has the same demands on the power input of the exhaust fan as an open exhaust flap in an apartment where the supply flap is also open.

The investor therefore has two series of values ​​for each apartment, one relating to the supply, the other relating to the exhaust. These two values ​​are further added and presented as one common - the total relative energy consumption for ventilation. The values ​​are available on the ContPort portal as cumulated and differential for any period, typically for the billing period (1 month).ContPort is an application for energy analysis and management of buildings and industrial facilities. It consists of three main modules:

An online data collection module that collects data from technologies either via visualization or directly from controllers. The values ​​are displayed on the portal on the overview page and are stored in the database. These data show how efficient the operation of the equipment is: the consumption of individual parts, ambient values ​​(sunlight, outdoor temperature, wind speed, etc.), process values ​​(temperatures, flows…) and energy consumption (electricity, gas, heat, water) are displayed. ). The values ​​are presented at the managerial level and are used for overviews and long-term planning.

The module for reporting and economic evaluation works with data obtained in the previous module or imported into the system from other sources (such as automatic import of meteodata from the Internet or a .csv file). It is possible to create different types of reports, from simple ones, such as an overview of operating costs of equipment for a certain period, to more complex mutual comparison of similar equipment (benchmarking) in different locations, related to units of measure (m2, kWp, years). Reports can be generated automatically and sent to recipients by e-mail.

The service help desk and administration provide complete archiving of technical and business documentation and the course of warranty, post-warranty and preventive inspections and interventions. The system stores the relevant documents necessary for safe and economical operation of buildings and technological units: project documentation, service and operational contracts, inspections, etc. The course of service intervention begins by reporting the problem - either manually via the web interface or automatically control and monitoring system. The service event is then processed, closed and invoiced. Preventive inspections are planned in advance and their service tickets are generated automatically. Part of this module is also the management of the spare parts warehouse. This module is not yet used for the action of Trade Unions 2.ContPort was designed for service and management companies and for investors managing multiple technologies, ie for users who want a comprehensive overview of costs and efficiencies. Service companies mainly use the application part, while their subcontractors access the system via the ContPort web portal at www.contport.com. The connection to the portal is encrypted and access to data is restricted according to user levels and their rights.