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ЗмістThe selection of a heat pump
DONETSK NATIONAL TECHICAL UNIVERSITY
PHYSICAL AND METALLURGICAL FACULTY
The application of the heat pumps for heat recovering
and in heating systems.
Probachai Oleksii, Safyants Artyom.
Research supervisor – Kolesnichenko Nazar
At present, the system of central heating in Ukraine is in a bad condition. In winter season, it constantly happens that the temperature in the buildings doesn’t meet the requirements of fixed norms, we can also observe the mass disconnecting of heat consumers from the heating system. In my native city Donetsk with its population of about 1 ml. people, there are 330 boiler houses, which often serve only 2 or 3 buildings instead of the whole neighbourhood. It’s natural that with such under loading of the boilers their efficiency is far from being maximal. Both this and very bad conditions of the heating systems lead to the enormous overrun of energy and, as a result, an overdraft of funds. That’s why it is necessary to find the solution for this problem.
Nowadays, the whole central heat supply system renovation suffers hard times and needs a more optimal approach. Our aim is to find out in what way it is better to develop the central heating system.
Here is the statistics of the Housing and Urban Development Ministry concerning different types of energy sources, HRU/yr
As you can see from the chart, implementing a heat plump (HP) as a heat source is the most economical and efficient. The savings make up 40000 HRU a year. In average, a HP can supply a house with heating, 60-75% of which being free of charge. In fact, the initial costs for a pump and its installation can make 600,000 HRU. But the capital outlay will have been paid back in 9 years minimum at the expense of saving fuel and electricity (we will observe the next increase in energy prices from January 1, 2009). The HP operation will last for 15-20 years before major overhaul.
The given research aims to estimate the individual heating system on the basis of HP and to carry out its optimization taking into account the amendment of now existing heat-circulation system and a back-up heat source, such as a boiler, of a boiler house.
As an object under research we take a 9-storied building of 1KG-480 type, which was put into operation in the 90s of the 20th century. Unlike a traditional water-air scheme (in which we use outdoor air only as a heat source with lower temperature) one could use the mixture of some heated air, coming from the ventilation system, with some cooler outdoor air – this mixture will increase the pump efficiency up to 1.3-1.4 times.
The research has two assignments:
1. To calculate total heat loss through ventilation system, walling, etc.
2. To develop measures for the increasing HP efficiency.
The building heat loss calculated as prescribed in Building Code 2.08.01.-87 can be seen in Chart 1.
Chart 1- Heat loss through ventilation system (calculations as to Building Code 2.08.01.-87)
The heat loss through walling is calculated in a standard way with the account of construction characteristics, such as wall gauge, surface of the building, its dimensions, panel heat conductivity etc. The control temperature points are -25, -20, -15, -10, -5, 0, +8, +13 0С.
Chart 2. - Heat Loss through the walling
The graph of the total heat load for an unheated building looks like this:
Chart 3- The Total Heat load
You should be careful while talking about the problem of the heat pump usage in Ukraine, because they are a rare thing nowadays. There are a lot of reasons for such rarity; the first one is a high price. We can also point out the underestimation of Ukraine as a potential outlet for the manufacturers of the heat pumps of the first-rate European firms (companies), there are also small investments in the advertisements of the given product on the territory of Ukraine, and natural gas price will rise in 2009. In spite of all these problems, there is an outlook for the heat pumps installation any way.
The application of heat pumps results into:
As for the shortcomings of the heat pumps, they are:
The quantity of the produced heat energy with a good potential can exceed the energy consumption up to 3-4 times. Since the typical efficiency of the present condensing plants is no more than 40%, the usage of the heating installations can be regarded to be the most economical one with the conversion ratio for no more than 2.5. It should also be admitted that the correlation between the thermal unit cost, produced with the help of the electric power, and the one produced from the usage of natural gas, is lower than 2.5, because in Ukraine the great amount of the electric power is produced from the usage of a cheaper solid and nuclear fuel.
The “air-water” heat pumps do not need lower outlines and while using them you do not have to dig a ditch or to drill a well.
Taking into account some limits dealing with the temperature of the outdoor air, HPs can be widely used as the only heat source in the regions with mild climate and it can also be used as the second more economical and environmentally friendly heat source added to the present systems on the basis of boilers. Using the technology of mixing the air from ventilation and the outdoor air, we decrease the HP cost.
According to Building Code 2.08.01-87, Building Code 2.08.02-89 etc. the temperature of the cold air of the most cold days is -150С for the 95% days of the heating period (season). While mixing the outdoor air of such temperature with the heated air from the ventilation system in proportion of 70% of the cold air to 30% of the heated air will cause the temperature of the mixture of -4.50С which will considerably decrease the cost of capital expenditures for HP. That’s why it is reasonable to select a heat pump according to the efficiency of the conversion ratio which will be in the limit of 2.3:3.5, and the first cost of the heat pump.
Chart 4-Annual Temperature in Ukraine
We need to extra reinforce the indoor ventilation system at transfer points, as well as to install a low-power receiver filter to allow removing the impurities from the air. This would add 4000 HRU more to the capital outlay, including installation work expenses.
Here is a graph of conversion ratio against minimum possible air mixture temperature which equals -12 0С if outdoor air temperature is -25 0С.
The next table compares a heat pump (HP) and a heating system (HS) as heat supply sources in regards to the cost of heating per hour.
Table 1. Heating characteristics – HP versus HS.
Heating Expenditure during a Heating Season.
Chart 6. Heating expenditure per 1 year (HRU/yr) –HP versus HS
As the chart shows, cost savings are obvious, which can reach 200,000 HRU/yr. However, the related capital outlay for the heat pump installation and its continuous operation maintenance is in the range between 2 and 3.3 million HRU. Thus, the payback time for such technology makes around 12-13 years, while its operation life lasts 15 years without a major overhaul. The profitability of a system like that is in doubt.
While using heat pumps for heating purposes one should be aware of their characteristic features. Firstly, external heat insulation of a building leads to the increasing of the Qvent-Qloss ratio, which results into a higher air mixture temperature and consequently a bigger conversion ratio for a heat pump. A HP can pay its cost only while operating in a properly heat insulated building with the heat loss not more than 100 watt/m2. The better the heat insulation, the more the cost savings are. To provide quick and cheaper thermo insulation we can use plates of plastic foam.
The estimated cost of thermo insulation including workforce expenses will make 97,000 HRU, which will decrease the specific heat loss up to 65-80 watt/m2.
Heat loss through insulated walling
Chart 7. Heat load of a heat insulated building.
Implementing the external heat insulation can decrease the heat load of a building which will need a heat pump with lower capacity and, thus, with a lower price.
40% of total heat loss is due to ventilation systems. As we know, heat pumps will use the air mixture for their operation. And if we calculate the minimum air mixture temperature (outdoor air and ventilation system air), possible in this climate, it will make -10 0С. Together with this, dealing with a smaller heat load and a more narrow range of air temperatures will reduce the capital outlay up to many times. Let us consider ClimateMaster (ROOFTOP) heat pump installation as an example. A 280 kilowatt pump installation will cost 780,000-80,000 HRU.
Table 2. Heating characteristics for a building with thermo insulation – HP versus HS
Heating Expenditure during a Heating Season.
Heating expenditure per 1 year (HRU/yr) –HP versus HS
As we can see from the chart, one can save 197,803 HRU a year using a heat pump independently.
In the following formula CT=CHP+Cmodern
CT is capital outlays total,
CHP is a heat pump cost, and
Cmodern is thermo insulation costs and district heating improvement costs.
The operating costs depend on the electricity prices, the duration of the heating season (that is the heat pump operation term) and the pump conversion ratio. Hence,
Э – base-load demand costs,
? – HP operation term,
µ - HP conversion ratio.
Thus, CT equals 931,000 HRU with the payback time making 5 years.
In general, we can state that HP application would become a way out from heating crisis in Ukraine, used for a separate building or even a number of buildings. However, from my point of view, the national scale requires a different solving of the problem, say, cogeneration, for instance.
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