【 Weak current College 】 air source heat pump system in domestic central air-conditioning applications (1)

With the improvement of living standard, people on the residential environment of increasingly demanding, especially on indoor air environment put increasingly higher demands. The initial people using window type air conditioner, split, wall-mounted, conditioners to reduce indoor temperature, but since there is no outdoor fresh air, indoor air quality to be guaranteed; split air conditioning of the outdoor unit and window type air conditioner installation reserve hole into damage buildings facades and destruction of the urban landscape. Moreover, in recent years, with the continuous improvement of living conditions, normal residential area was expanded to 90 ~ 200m?, some even reach the Villa and apartment 500 ~ 600m?, apparently conditioner has less and less adapted to the more upmarket residential development needs, home air conditioning has emerged.

At present the typical household central air conditioning systems in general there are three types: residential air supply central air-conditioning system, household frequency with central air conditioning system, ventilation tube household central air-conditioning system. From our present technological level and air conditioning production conditions, air source household central air-conditioner system more suitable to China's national conditions. The following focuses on household air source heat water air conditioning system and need to be aware of the problem.

1. system cooling load and thermal load and equipment selection

Calculates residential cooling load, since all terminal equipment at the same time use of chance, the total calculation system cooling load, according to user requirements and usage properties to consider different usage factor. Heating time, according to different heating mode to select both coefficients and consider the effect of the heat transfer between. After you determine the total cooling load and thermal load under this area of meteorological conditions and the energy supply situation for reasonable equipment choices, such as air source water chiller, air source single cold unit + water heaters, air source single cold unit + urban heat source, etc. Indoor terminal equipment generally fan-coil and air handling unit, the selection of terminal equipment should be considered when intermittent use coefficient of 1.2 and 1.2 Pro room without air conditioning in the envelope when you load additional coefficient.

Selection of air supply unit should be local to select the best balance. Best balance select unit of general steps:

① calculation to balance the temperature of the thermal load of the building.

② the equilibrium temperature for quantity of heat, conversion to standard conditions of heating select air source water chiller.

③ by querying the manufacturers of samples or technical information, find the line in the winter and air conditioning system design of heating and the heat load by design seek auxiliary heat source capacity.

④ by querying the manufacturers samples or technical information, find the unit in daylight and air-conditioning design condition of cooling capacity, if you do not meet the requirements of the air-conditioning cooling load, you should add a secondary cold source, taking into account the convenience of cold machine layout, General selection of air-cooled single cold units for secondary cold source

According to this method selects the unit, as a rule there will be no summer air-conditioning design conditions heat pump unit provides cooling capacity than air-conditioning design cooling load.

2. air supply unit for defrosting

For reasons known to all, the application of the air source is affected by climatic conditions, in the heat pump technology more leading Japan has a number of "heating degree days HDD < 3000" recommended standard, range of use in China once delineated in the lower reaches of the Yangtze River, the present guidance on a variety of engineering design documents will winter outdoor design temperature tw =-3? C minimum line ordering. However in the last ten years of its application to the northern extension of the trend is obvious, Xi'an, Zhengzhou, Yantai, Beijing and other cities have many applications.

Have researchers made a calculation of air-water heat pumps in dry and wet conditions change critical humidity and moisture frosting critical methods, established for the two critical relative humidity of the air source model for solving different water temperatures and different air temperatures in these two critical humidity value, draw out the use of air-water heat pump when the frosting regional and dry conditions. 45? C water, air source unit run time frosting regional and dry conditions of approximate regional line towards — along the Lhasa — Shijiazhuang Taiyuan Lanzhou — — Jinan first line. This line to the North of the regional air source to the runtime, no frosting; while this South, unit there are varying degrees of frosting.

In the air source unit with regard to the mechanism for Frost in recent years has also carried out experimental study related to the study results show that air side heat exchanger frosting, not only the cream of thickness changes, cream of density is also changing, just started frosting, frosting volume mainly increased Frost thickness and density change is very small. Over time, Frost thickness increased slow down the increase in the density and density of frost

The time is a parabola law changes. Study results show that in different conditions, air side heat exchanger frosting the situation is different. When the air temperature, relative humidity, the greater must be the more serious the frosting defrosting time interval is shorter; the relative humidity in the air, surely? 0 C condition 4 than-frosting? C condition of severe frost.

Low temperature for heating the run-time defrosting, to prevent deterioration due to the accumulation of frost layer evaporator heat process. Obviously, the air source-to-water defrost control method of timing control method is not consistent with Frost thickness variation over time. Similarly, many manufacturers are using time-temperature control method, or harmonization of fixed defrost starting value and defrosting time values as air temperature, relative humidity, the thickness of the Frost, defrost the effect is different. Frosting for correct predictions and master, is the guarantee for defrosting to good effect. Ideal for defrosting procedures should be both at the time when frost accumulation without defrosting in frost-free invalid when defrosting. Current common defrosting method in addition to time control and time-temperature control method, by-pass defrosting method, pressure control, inverter compressor and electronic expansion valve of the heat pump unit of sensible heat defrosting and MP99 computer defrosting, smart defrost, fuzzy defrosting, etc., of reliable efficient defrosting technology, is the development and promotion of domestic airAir conditioning system of key technologies.

In the manufacturers product samples, the heat pump for heating only is the standard mode of instantaneous heat, when the coil frosting, unit efficiency decrease rapidly, so the air source unit winter heating should be calculated according to the outdoor air temperature correction coefficients and error correction, be corrected by the following formula: Q = q · K2 · K1 (-, Q-unit heating Kw; q-product samples of instantaneous heating Kw; K1-use area outdoor air conditioning calculations dry-bulb temperature correction coefficient, select by product samples; K2 unit defrosting correction coefficient, defrosting once per hour from 0.9, second of 0.8).